Merge torrust#833: refactor: replace text-to-png with internal render-text-as-image and modernize codebase

f326874 test: add comprehensive test coverage for render-text-as-image and related components (Cameron Garnham)
67e411f refactor: replace text-to-png with internal render-text-as-image and modernize codebase (Cameron Garnham)

Pull request description:

  Replace the external `text-to-png` dependency with a new internal `render-text-as-image` package, modernizes the codebase by migrating from `lazy_static` to `std::sync::LazyLock`, relocates unit tests to a centralized `src/tests/` directory, and bumps the minimum Rust version from 1.72 to 1.80.

  ## Key Changes

  ### Dependency Modernization
  - **Replaced `text-to-png`** with new internal `render-text-as-image` package
    - Pure-Rust text-to-PNG rendering using `ab_glyph` + `image` crates
    - Embedded Roboto Mono font (no system dependencies)
    - Eliminates heavy SVG rendering pipeline (resvg, usvg, fontdb, rustybuzz, etc.)
    - Reduces transitive dependencies by ~30+ crates
  - **Replaced `lazy_static`** with `std::sync::LazyLock` (stable since Rust 1.80)
  - **Updated `io::Error::new(...)`** to `io::Error::other(...)` (stable since Rust 1.74)
  - **Consolidated `bitflags`** from v1 + v2 to v2 only
  - **Bumped minimum Rust version** from 1.72 to 1.80 (required for LazyLock)

  ### New Internal Package: `render-text-as-image`
  - Self-contained text rendering library for containerized environments
  - Modular architecture: blend, encode, font, layout, render, types modules
  - Comprehensive documentation: specification (§SPEC R-1) and ADRs (001–003)
  - Includes embedded Roboto Mono Regular font (125KB TTF)
  - Designed for CAPTCHA, image generation, and similar use cases

  ### Test Architecture Reorganization
  - **Moved inline `#[cfg(test)]` modules** to centralized `src/tests/` directory
  - Follows project convention of separating crate-level tests from source
  - Affected modules: config, cache, mailer, models, services, tracker, utils
  - Updated `src/lib.rs` to include `mod tests;` for test discovery
  - Some items widened to `pub(crate)` visibility to support test access

  ### Workspace Configuration
  - Converted project to Cargo workspace with three members:
    - Main `torrust-index` crate
    - `located-error` package
    - `render-text-as-image` package
  - Updated `Cargo.toml` with workspace inheritance for metadata

  ### Code Quality Improvements
  - **Fixed recurring typos**: "migth" → "might", "becuase" → "because", "successfull" → "successful", "Ununauthorized" → "Unauthorized"
  - Updated `.gitignore` to exclude test report files
  - Updated `cspell.json` and `project-words.txt` with new vocabulary
  - Expanded `AGENTS.md` with detailed development guidelines

  ## Benefits
  - **Reduced dependency tree**: ~30+ transitive crates removed
  - **Modern Rust idioms**: Uses stable stdlib features (LazyLock, io::Error::other)
  - **Better test organization**: Clear separation between source and test code
  - **Self-contained text rendering**: No external system dependencies (FreeType, Fontconfig)
  - **Improved compile times**: Smaller dependency graph and modular test structure

  ## Testing Performed
  - All existing tests continue to pass after migration
  - New `render-text-as-image` package includes comprehensive unit tests
  - Crate test structure validated with `cargo test --workspace`

  ## Breaking Changes
  - **Minimum Rust version increased from 1.72 to 1.80**
    - Required for `std::sync::LazyLock` and `io::Error::other()`
    - Rust 1.80 was released in July 2024 (~1.5 years ago)
  - No API changes to public interfaces

  ## Migration Needed
  - Developers must update to Rust 1.80+ to build the project
  - New test contributions should follow the centralized `src/tests/` pattern
  - Text rendering functionality now uses the internal `render-text-as-image` API

  ## References
  - `std::sync::LazyLock` stabilization (Rust 1.80, July 2024)
  - `io::Error::other()` stabilization (Rust 1.74, October 2023)
  - Specification for render-text-as-image (§SPEC R-1)
  - ADR 001–003 for dependency, font, and structure decisions

ACKs for top commit:
  da2ce7:
    ACK f326874

Tree-SHA512: 97db8fa981a5538807611c46b39f118d1aee617eda7ca324b713a3793b17294f0550f9ec8e06d0a6b06657012826d2c60c0eaca9501759918d9953d76d69681b

Author: da2ce7

.github/workflows/e2e.yaml

@@ -1,4 +1,4 @@
-# Temporary execution of E2E tests using MySQL becuase it's failing
+# Temporary execution of E2E tests using MySQL because it's failing
 # in the `testing.yml` workflows and affects deployments and releases.
 # See https://github.com/torrust/torrust-index/issues/580
 name: E2E Testing

.github/workflows/upload_coverage_pr.yaml

@@ -1,7 +1,7 @@
 name: Upload Coverage Report (PR)
 
 on:
-  # This workflow is triggered after every successfull execution
+  # This workflow is triggered after every successful execution
   # of `Generate Coverage Report` workflow.
   workflow_run:
     workflows: ["Generate Coverage Report (PR)"]

.gitignore

@@ -7,4 +7,6 @@
 /output/
 /storage/
 /target
-/uploads/
+/uploads/
+**/*report.txt
+**/*report.diff

AGENTS.md

@@ -2,4 +2,56 @@
 
 ## Cargo Commands
 
-Prefer using `--workspace --all-targets --all-features` when running `cargo check`, `cargo clippy`, or `cargo test`.
+Prefer using `--workspace --all-targets --all-features` when running
+`cargo check`, `cargo clippy`, or `cargo test`.
+
+Be mindful to at least do a quick spot-test with `--no-default-features`,
+and to try building the docs and running the doc-tests.
+
+When testing, also run the tests in `--release` mode to check that this
+works. Run the tests in debug mode with `CARGO_PROFILE_DEV_OPT_LEVEL=3`;
+otherwise it is just too slow. You can turn off the optimisation if a bug
+is found and you need backtracing.
+
+When working inside a package, prefer running only the `--package` tests,
+as the whole-project tests are slow to run. (Occasionally run the whole
+suite, for example when finishing up.)
+
+## Running Tests
+
+When running tests, tee to a temp file (`/tmp/...`) and then grep that
+file after the tests have completed.
+
+## Test Locations
+
+We use three levels of tests based upon viability. In general, crate tests
+are preferred over unit tests. Integration tests should test the public
+API, perhaps using `#[doc(hidden)]` helpers when appropriate.
+
+| Level       | Visibility   | Location      |
+|-------------|--------------|---------------|
+| Unit        | `private`    | inline        |
+| Crate       | `pub(crate)` | `/src/tests/` |
+| Integration | `pub`        | `/tests/`     |
+
+## Cross-Reference Conventions
+
+Eagerly corrected when spotted in **any** file!
+
+Cross-references use the `§` (section sign) prefix. Every reference
+carries a **package qualifier** — `T-` for Torrust —
+so the target document is never ambiguous.
+
+### General Rules
+
+- Use `§§` for ranges: e.g. `§§ALGO M-12.2–12.5`.
+- Bare `§N` (no label) is acceptable **within** a document that already
+  establishes context (e.g. inside `algorithm.md` itself), but in source
+  code and cross-package references always use the fully qualified
+  `§BOOK PACKAGE_PREFIX-N` form.
+
+## Replacing a File
+
+1. Read the file.
+2. Using the CLI, `rm` the file.
+3. Recreate the file.