docs(bf-146g8): verify miroir-proxy builds + 29G free-disk pre-flight

Foundation step for bf-ml7fg verify-only decomposition. Confirmed
cargo build -p miroir-proxy exits 0 with the in-tree extract_source_ip
fix; no compile fixes needed. Pre-flight disk check recorded 29G free
(above the ~20G threshold, no target/ clearing required).

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

notes/bf-146g8.md

@@ -0,0 +1,38 @@
+# Bead bf-146g8: Verify miroir-proxy builds + free-disk pre-flight
+
+## Issue
+Split-child of bf-ml7fg (verify-only decomposition). Foundation step: confirm the
+`miroir-proxy` crate compiles before any tests run. The fix (search-UI per-IP rate
+limiting via `extract_source_ip`) is ALREADY in the uncommitted working tree — this
+bead does NOT reimplement it, only verifies the build.
+
+## Pre-flight: free disk
+Per `~/CLAUDE.md`, checked free space on `/` before building:
+
+```
+df -BG --output=avail /  →  29G
+```
+
+29G > ~20G threshold → no need to clear an idle `target/` from another repo.
+
+## Verification
+- `cargo build -p miroir-proxy` → **exit 0** (no errors, no warnings).
+- Confirmed the changed source actually compiled (not a stale cache): touched
+  `crates/miroir-proxy/src/routes/search.rs` and rebuilt — `libmiroir_proxy.rlib`
+  and the `miroir-proxy` binary mtimes advanced past the source mtime, and a
+  follow-up `cargo check -p miroir-proxy` → exit 0.
+- The changed code (`pub fn extract_source_ip`, `pub fn hash_for_log`, and the
+  threaded `source_ip` parameter through `search_handler` → `search_multi_targets`)
+  compiles cleanly.
+
+## Result
+Build-only scope satisfied. **No compile fixes were needed** — the fix already in
+the working tree was correct. The uncommitted fix files
+(`crates/miroir-proxy/src/routes/search.rs`, the new
+`crates/miroir-proxy/tests/search_ui_rate_limit.rs`, `CHANGELOG.md`) belong to the
+parent bead bf-ml7fg and were intentionally left uncommitted here.
+
+## Acceptance criteria
+- [x] Free disk checked before build; GB free recorded (29G)
+- [x] `cargo build -p miroir-proxy` exits 0
+- [x] No changes to extraction logic; only compile fixes if any (none needed)