chore: remove serena leftovers (hooks, permissions, docs, templates) (#8518)

## Summary

Serena MCP was removed from the project, but config and docs still
referenced it. The most visible symptom: every Claude Code session
failed on startup with

```
SessionStart:startup hook error
Failed with non-blocking status code: /bin/sh: 1: serena-hooks: not found
```

This completes the removal:

- **`.claude/settings.json`**: drop all `serena-hooks` hooks (PreToolUse
remind/auto-approve, SessionStart activate, Stop cleanup) and the
`mcp__serena__*` permission entry
- **`.serena/`**: delete the tracked project files and memories (were
already deleted locally, now committed)
- **`CLAUDE.md`**: remove the Serena tool section; Context7 guidance
kept
- **`agentic/commands/`**: replace Serena tool references
(`mcp__serena__*`, `list_dir`, `find_file`, `search_for_pattern`,
`think_about_collected_information`) with built-in Glob/Grep/Read/Edit
equivalents across the audit auditors, `audit.md`, `agentic.md`,
`prime.md`, `prime-deep.md`, and `audit.workflow.js`

Historical artifacts (`agentic/runs/`, `agentic/audits/`,
`agentic/specs/`) intentionally untouched.

## Verification

- `grep -rni serena` over the repo (excluding historical artifacts)
returns zero hits
- Both settings files validate as JSON
- The local untracked `.claude/settings.local.json` was cleaned
separately (not part of this PR)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: MarkusNeusinger

.claude/settings.json

@@ -8,7 +8,6 @@
       "Read(/tmp/*)",
       "mcp__plugin_context7_context7__*",
       "mcp__plugin_playwright_playwright__*",
-      "mcp__serena__*",
       "Bash(git commit *)",
       "Bash(git push *)"
     ],
@@ -17,49 +16,5 @@
   },
   "env": {
     "CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS": "1"
-  },
-  "hooks": {
-    "PreToolUse": [
-      {
-        "matcher": "",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "serena-hooks remind --client=claude-code"
-          }
-        ]
-      },
-      {
-        "matcher": "mcp__serena__*",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "serena-hooks auto-approve --client=claude-code"
-          }
-        ]
-      }
-    ],
-    "SessionStart": [
-      {
-        "matcher": "",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "serena-hooks activate --client=claude-code"
-          }
-        ]
-      }
-    ],
-    "Stop": [
-      {
-        "matcher": "",
-        "hooks": [
-          {
-            "type": "command",
-            "command": "serena-hooks cleanup --client=claude-code"
-          }
-        ]
-      }
-    ]
   }
 }