docs(readme): convert README.adoc -> Markdown README.md (#30)

README must be real Markdown to render in GitHub community-health, the GitHub
profile, and external MCP directories (Glama) — AsciiDoc shows as raw markup
there. pandoc asciidoc->GFM, badges fixed to clickable, SPDX header kept as an
HTML comment, duplicate README.adoc removed.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

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+<!--
+SPDX-License-Identifier: CC-BY-SA-4.0
+SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+-->
+
+# What Is This?
+
+Halideiser compiles image and video processing pipelines to optimised
+[Halide](https://halide-lang.org) schedules. You describe your pipeline
+stages in `halideiser.toml` — blur, sharpen, resize, edge detect, colour
+transform, convolution — and Halideiser generates the Halide algorithm
+definitions, auto-tunes the schedule for your target hardware, and
+produces optimised native code.
+
+Halide (by Jonathan Ragan-Kelley et al., MIT/Google) separates the
+*algorithm* (what to compute) from the *schedule* (how to compute it on
+hardware). This separation enables 10–100x speedups over hand-tuned C by
+letting the compiler explore tiling, vectorisation, parallelism, and
+memory layout choices automatically. Halideiser makes this power
+accessible without Halide expertise.
+
+# How It Works
+
+```text
+halideiser.toml         (pipeline description)
+       │
+       ▼
+  Pipeline Parser       (validate stages, data flow, dimensions)
+       │
+       ▼
+  Idris2 ABI Proofs     (prove pipeline correctness, buffer safety)
+       │
+       ▼
+  Halide Algorithm       (Func definitions, Var bindings, Expr trees)
+  Codegen                (from pipeline stages)
+       │
+       ▼
+  Schedule Generation    (tile, vectorize, parallelize, compute_at,
+  + Auto-Tuning          store_at, reorder — search over schedule space)
+       │
+       ▼
+  Compiled Pipeline      (native code for target hardware)
+```
+
+1.  **Describe** your pipeline in `halideiser.toml` — stages, buffer
+    dimensions, data types, target hardware
+
+2.  **Validate** — the Idris2 ABI layer formally proves buffer bounds,
+    dimension compatibility, and stage connectivity
+
+3.  **Generate** — Halide algorithm code is emitted with `Func`, `Var`,
+    and scheduling primitives
+
+4.  **Tune** — the auto-tuner searches the schedule space (tile sizes,
+    loop orders, parallelism) for optimal performance
+
+5.  **Compile** — the tuned schedule is compiled to native code via LLVM
+
+# Halide Concepts
+
+Halideiser works with core Halide abstractions:
+
+- **Func** — a pure function defining what to compute at each pixel
+
+- **Var** — a dimension variable (x, y, channel, frame)
+
+- **Scheduling primitives** — control *how* to execute:
+
+  - `tile(x,` `y,` `xi,` `yi,` `tx,` `ty)` — break loops into tiles for
+    cache locality
+
+  - `vectorize(xi,` `width)` — use SIMD instructions (SSE, AVX, NEON)
+
+  - `parallelize(y)` — distribute rows across CPU cores
+
+  - `compute_at(consumer,` `var)` — fuse producer into consumer loop
+
+  - `store_at(consumer,` `var)` — control where intermediate buffers
+    live
+
+  - `reorder(vars…)` — change loop nesting order
+
+  - `unroll(var,` `factor)` — unroll inner loops
+
+  - `gpu_blocks` `/` `gpu_threads` — map to GPU compute grids
+
+# Hardware Targets
+
+| Target       | Instructions / Backend               |
+|--------------|--------------------------------------|
+| x86 SSE/AVX  | 128–512-bit SIMD, auto-vectorisation |
+| ARM NEON/SVE | Mobile and embedded SIMD             |
+| CUDA         | NVIDIA GPU kernels                   |
+| OpenCL       | Cross-vendor GPU compute             |
+| WebAssembly  | Browser-based image processing       |
+| Metal        | Apple GPU compute                    |
+| Vulkan       | Cross-platform GPU compute           |
+
+# Key Value
+
+- **10–100x faster** image and video processing without writing Halide
+  by hand
+
+- **Automatic hardware scheduling** — SIMD, GPU, multi-core, all derived
+  from one pipeline description
+
+- **No Halide expertise needed** — describe the pipeline, get the speed
+
+- **Formally verified** — Idris2 proofs guarantee buffer bounds and
+  dimension safety before codegen
+
+- **Multi-target** — one pipeline compiles to x86, ARM, CUDA, OpenCL,
+  WebAssembly
+
+# Use Cases
+
+- **Real-time video filters** — blur, sharpen, colour grade at 60fps+
+
+- **Batch image processing** — resize, watermark, convert millions of
+  images
+
+- **Medical imaging** — CT/MRI reconstruction, denoising, segmentation
+
+- **Computational photography** — HDR merge, demosaicing, lens
+  correction
+
+- **Computer vision preprocessing** — edge detection, histogram
+  equalisation, feature extraction
+
+# Architecture
+
+Follows the hyperpolymath -iser pattern (same as
+[Chapeliser](https://github.com/hyperpolymath/chapeliser)):
+
+- **Manifest** (`halideiser.toml`) — describe WHAT pipeline stages you
+  need
+
+- **Pipeline Parser** (`src/manifest/`) — validate stage connectivity
+  and buffer dimensions
+
+- **Idris2 ABI** (`src/interface/abi/`) — formal proofs of pipeline
+  correctness, buffer layout, and scheduling safety
+
+- **Halide Codegen** (`src/codegen/`) — emit Halide `Func` / `Var`
+  definitions and scheduling calls
+
+- **Zig FFI** (`src/interface/ffi/`) — C-ABI bridge for calling compiled
+  pipelines from any language
+
+- **Rust CLI** (`src/main.rs`) — orchestrates parse, validate, generate,
+  tune, and build
+
+User writes zero Halide code. Halideiser generates everything.
+
+Part of the [-iser family](https://github.com/hyperpolymath/iseriser) of
+acceleration frameworks.
+
+# Status
+
+**Pre-alpha.** Architecture defined, scaffolding in place, codegen
+pending. Codebase in progress — pipeline parser and Halide codegen are
+next.
+
+# Quick Start
+
+```bash
+# Initialise a manifest in the current directory
+halideiser init
+
+# Edit halideiser.toml to describe your pipeline stages
+
+# Validate the manifest
+halideiser validate
+
+# Generate Halide code and schedule
+halideiser generate
+
+# Build the compiled pipeline
+halideiser build --release
+
+# Run the pipeline
+halideiser run -- input.png output.png
+```
+
+# License
+
+SPDX-License-Identifier: CC-BY-SA-4.0