feat(cli): add --progress flag for live indexing progress output

[halindrome]

Summary

Adds a `--progress` flag to the CLI that shows live, human-readable progress on stderr while keeping the JSON result on stdout unchanged.

```
$ codebase-memory-mcp cli --progress index_repository '{"repo_path":"/path/to/repo"}'
Discovering files (6402 found)
Starting full index
[1/9] Building file structure
Extracting: 6300/6402 files (98%)
[2/9] Extracting definitions
[3/9] Building registry
[4/9] Resolving calls & edges
[5/9] Detecting tests
[6/9] Scanning HTTP links
[7/9] Analyzing git history
[8/9] Linking config files
[9/9] Writing database
Done: 71645 nodes, 106757 edges (9422 ms)
{"project":"...","status":"indexed","nodes":71645,"edges":106757}
```

Design

No pipeline changes. Implementation registers a custom log sink via `cbm_log_set_sink()` in `run_cli()` that maps existing structured log events (`pass.start`, `pass.timing`, `pipeline.done`, etc.) to human-readable phase labels. When a sink is registered it becomes the sole output handler — the default `fprintf(stderr, ...)` is suppressed, keeping stderr clean.

Key implementation details:

• `src/cli/progress_sink.c` / `.h` — new log sink; maps 9 pipeline events to phase labels
• `src/main.c` — detects `--progress` in argv, installs sink before `cbm_mem_init()` (so even `mem.init` is suppressed), wires SIGINT → `cbm_pipeline_cancel()` for clean Ctrl-C
• `src/foundation/log.c` — when a sink is registered it replaces (not supplements) the default stderr output
• Parallel extraction path shows in-place `\r` counter: `Extracting: N/M files (X%)`
• Incremental no-op path exits cleanly after two lines
• Node counts sourced from `gbuf.dump` event (fired before `node_by_qn` is freed) rather than `pipeline.done` (which always has `nodes=0` after the hash table free)

Test plan

• `codebase-memory-mcp cli --progress index_repository '{"repo_path":"..."}'` — stderr shows phase labels, stdout has clean JSON
• Large repo (>500 files, parallel path): `Extracting: N/M files (X%)` counter appears in-place
• Incremental no-op: only "Discovering files" + "Starting incremental index" appear
• Without `--progress`: structured `level=info` log lines still appear on stderr (unchanged)
• 2046 tests pass
• Ctrl-C during indexing: pipeline cancelled cleanly

🤖 Generated with Claude Code