feat(mcp): line numbers in explore output + per-file cluster fixes (#188)

* feat(mcp): line numbers in explore output + per-file cluster fixes

Follow-up to #185. Three changes to codegraph_explore:

1. Source sections now carry cat -n style line-number prefixes
   (<num>\t<code>), so the agent can cite file:line straight from the
   payload instead of re-Reading the file just to recover a line number.
   Isolated A/B: the no-line-numbers arm spent 2 Reads + a grep to find a
   line number the line-numbered arm cited with zero follow-up calls.
   Payload cost ~3-5%. Toggle off with CODEGRAPH_EXPLORE_LINENUMS=0.

2. Per-file cluster selection now ranks clusters containing a query entry
   point ahead of dense declaration blocks. Density-only ranking buried
   the relevant methods (perform/didCreateURLRequest/task in Alamofire's
   Session.swift) under the top-of-file class header + property list.

3. Whole-file "envelope" nodes (a class/struct/etc. spanning >50% of the
   file) are excluded from clustering. The Session class spans ~1,400
   lines; keeping it collapsed every method into one giant cluster that
   tail-trimmed down to just the class header, hiding the methods.

Net vs the 0.7.10 baseline, line numbers on: Alamofire -60%, Excalidraw
-32%, VS Code -12% per explore call.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(mcp): language-neutral omission markers in explore output

The gap separator and the two tail-trim markers used C-style `//`
comments, which aren't comments in Python, Ruby, etc. Switch to plain
`... (gap) ...` / `... (trimmed) ...` so they read correctly inside any
language's fenced source block. With line numbers on, the line-number
jump already corroborates a gap.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(mcp): language-neutral truncation marker in codegraph_context

Sibling to the explore marker fix: codegraph_context's code-block
truncation used a C-style `// ... truncated ...`. Switch to
`... (truncated) ...` so it reads correctly in any language's fenced
source block.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* chore(release): bump version to 0.7.11

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@colbymchenry/codegraph",
-  "version": "0.7.10",
+  "version": "0.7.11",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@colbymchenry/codegraph",
-      "version": "0.7.10",
+      "version": "0.7.11",
       "license": "MIT",
       "dependencies": {
         "@clack/prompts": "^1.3.0",