fix(agents): remove invalid tool names across multiple agents 🤖🤖🤖 (#1384)

Remove or replace tool names that VS Code Copilot silently ignores
because they do not exist in the current built-in tools reference.

Files changed:
- context-architect: 'codebase', 'terminalCommand' → proper namespaced tools
- debug: 'web/githubRepo', bare 'search' → remove/replace
- implementation-plan: 'think', 'search/changes', 'findTestFiles',
  'search/searchResults', 'web/githubRepo', 'execute/runNotebookCell',
  'read/getNotebookSummary', 'read/readNotebookCellOutput', bare 'search' → remove
- janitor: 'browser', 'microsoft.docs.mcp/*', 'read/getTaskOutput' →
  remove browser & mcp wildcard; move getTaskOutput to execute/ namespace
- plan: 'web/githubRepo', 'azure-mcp/search', 'search/searchResults' → remove
- principal-software-engineer: 'browser' → remove
- specification: old-style bare tool names → correct namespaced equivalents

Reference: https://code.visualstudio.com/docs/copilot/reference/copilot-vscode-features#_chat-tools

Co-authored-by: Ming <oncwnuAUeYAFR4UGlq8BEJq8Jy-k@git.weixin.qq.com>

agents/plan.agent.md

@@ -5,9 +5,7 @@ tools:
   - search/codebase
   - vscode/extensions
   - web/fetch
-  - web/githubRepo
   - read/problems
-  - azure-mcp/search
   - search/searchResults
   - search/usages
   - vscode/vscodeAPI