Release: v1.0 preview — core rewrite, CI/CD, docs, and test suite overhaul (#159)

## Overview

Promotes `develop/1.0` to `preview/1.0` in preparation for the 1.0
preview release. This batch brings in a full rewrite of the library's
core, docs, CI/CD pipeline, and test suite accumulated since the last
preview snapshot.

## What's included

### 🏗️ CI/CD & Workflows
- **New workflows**: `bump-version`, `promote-branch` with source-branch
enforcement, auto merge-to-main on release
- **Branch protection**: new `lock`/`unlock` composite actions;
`preview/**` and `release/**` branches are now automatically locked
after creation
- **Fix**: removed invalid `administration` permission from
`release.yml` that caused workflow parse failures (#158)
- **Fix**: corrected pull-request-finding logic in promote workflow
- **Docs publishing**: URL-aware version switcher via `docs-versioning`
template; `versions.json` manifest; reworked `generate-docs` job (#157)

### 📚 Documentation
- New `/docs` developer guides: local development, testing conventions,
benchmarks, composite actions catalogue, CI workflow reference, branch
strategy, versioning pipeline, API doc generation, extensibility guide
(#155)
- Updated API reference YAMLs for version 1.0
- Fixed grammar, TOC typo, and outdated API references in docs
- Updated `CONTRIBUTING.md` with links to all new docs articles
- Flushed `PublicAPI.Unshipped.txt`

### 🔧 Source (library)
- Refactored internal structure: `CoordinateDelta`,
`CoordinateVariance`, `Pow10`, `Defaults`, `ExceptionGuard`, logging
helpers
- Updated `PolylineEncoder`, `PolylineDecoder`, `PolylineEncoding`,
`PolylineEncodingOptions`, `PolylineEncodingOptionsBuilder`
- Public API cleanup; `.editorconfig` updated (primary constructors
disabled)

### ✅ Tests
- Reorganized test files into proper namespace folders (`Abstraction/`,
`Extensions/`, `Internal/`)
- Added new test classes for `CoordinateDelta`, `CoordinateVariance`,
`Pow10`, `ExceptionGuard`, `LogDebugExtensions`, `LogWarningExtensions`,
`InvalidPolylineException`, `PolylineEncodingOptionsBuilder`, and
encoder/decoder extensions
- Removed stale/duplicate test files

### 🛠️ Build & Config
- Cleaned up `PolylineAlgorithm.slnx`, `Directory.Build.props`,
benchmarks config
- Updated `.gitignore` to exclude dynamically generated
`api-reference/_docs/`
- Misc cleanup (removed junk files, updated `AGENTS.md`)

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: Pete Sramek <petr.sramek@dropoutcoder.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: 6 people