Add CLAUDE.md with versioned changelog, update README

- Created CLAUDE.md with instructions to update changelog and README on
  every commit, version number (v1.2.0), and full changelog from v1.0.0
- Updated README: document-scope BLIGHT:: syntax, processing order,
  two-line failure format, complete_document() in AI provider section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,45 @@
+# CLAUDE.md — BLIGHT: CUE
+
+## Instructions for Claude
+
+- **Every commit**: Update the Changelog section below with a summary of what changed and bump the version number if appropriate.
+- **Every commit**: If the changes affect anything documented in README.md (trigger syntax, failure behavior, setup, project structure, AI provider info, etc.), update README.md in the same commit.
+
+---
+
+## Version
+
+**v1.2.0**
+
+---
+
+## Changelog
+
+### v1.2.0
+- Fixed loop re-processing: AI responses are sanitized by replacing `BLIGHT:` with `BLIGHT:` before being written to the document, preventing the service's own commits from triggering another processing cycle.
+- Branch awareness: branch is now extracted from `refs/heads/<branch>` in the push payload and passed to all Gitea read/write calls, so pushes to non-default branches are handled correctly.
+- Commit messages now include the file path (e.g. `BLIGHT: process triggers in notes/todo.md`).
+
+### v1.1.0
+- Added `BLIGHT::` (double colon) document-scope trigger syntax. Unlike `BLIGHT:` which replaces only the trigger line, `BLIGHT::` replaces the entire file content with the AI's rewritten document.
+- Multiple `BLIGHT::` triggers in one file are processed sequentially, each operating on the result of the previous.
+- Inline `BLIGHT:` triggers are always processed before `BLIGHT::` triggers.
+- Both trigger types are now case-insensitive (`blight:`, `BLIGHT:`, `Blight::`, etc. all match).
+- Failure comments updated to two-line format:
+  ```
+  <!-- BLIGHT_FAILED: <instruction> -->
+  <!-- BLIGHT_ERROR: <error message> -->
+  ```
+- Added `complete_document()` to `AIProvider` ABC and `GeminiProvider`, with a dedicated system prompt instructing the model to return the full rewritten document.
+
+### v1.0.0 — Initial release
+- Flask webhook server listening for Gitea push events.
+- HMAC-SHA256 signature verification on all incoming webhooks.
+- Scans changed `.md` files for `BLIGHT: <instruction>` trigger lines.
+- Sends full document + instruction to Google Gemini 2.5 Flash-Lite.
+- Replaces trigger line with AI response in-place and commits back to Gitea.
+- Retry logic: 3 attempts with exponential backoff (1s, 2s, 4s).
+- Processes webhooks in background threads to return 200 immediately.
+- Deduplicates file paths across multiple commits in a single push.
+- Self-updates on startup via `git pull --ff-only`.
+- Pluggable `AIProvider` ABC for swapping AI backends.