fix(install): chmod sdk dist/cli.js executable; fix context monitor over-reporting (#2460)

Bug #2453: After tsc builds sdk/dist/cli.js, npm install -g from a local
directory does not chmod the bin-script target (unlike tarball extraction).
The file lands at mode 644, the gsd-sdk symlink points at a non-executable
file, and command -v gsd-sdk fails on every first install. Fix: explicitly
chmodSync(cliPath, 0o755) immediately after npm install -g completes,
mirroring the pattern used for hook files throughout the installer.

Bug #2451: gsd-context-monitor warning messages over-reported usage by ~13
percentage points vs CC native /context. Root cause: gsd-statusline.js
wrote a buffer-normalized used_pct (accounting for the 16.5% autocompact
reserve) to the bridge file, inflating values. The bridge used_pct is now
raw (Math.round(100 - remaining_percentage)), consistent with what CC's
native /context command reports. The statusline progress bar continues to
display the normalized value; only the bridge value changes. Updated the
existing #2219 tests to check the normalized display via hook stdout rather
than bridge.used_pct, and added a new assertion that bridge.used_pct is raw.

Closes #2453
Closes #2451

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

hooks/gsd-statusline.js

@@ -147,10 +147,15 @@ function runStatusline() {
       if (sessionSafe) {
         try {
           const bridgePath = path.join(os.tmpdir(), `claude-ctx-${session}.json`);
+          // used_pct written to the bridge must match CC's native /context reporting:
+          // raw used = 100 - remaining_percentage (no buffer normalization applied).
+          // The normalized `used` value is correct for the statusline progress bar but
+          // inflates the context monitor warning messages by ~13 points (#2451).
+          const rawUsedPct = Math.round(100 - remaining);
           const bridgeData = JSON.stringify({
             session_id: session,
             remaining_percentage: remaining,
-            used_pct: used,
+            used_pct: rawUsedPct,
             timestamp: Math.floor(Date.now() / 1000)
           });
           fs.writeFileSync(bridgePath, bridgeData);