feat(tools): glob + grep read-only workspace search tools

Weak local models reached for shell find/grep -r (unjailed, dumps
.gitignore'd trees, floods context) to answer 'does frontend/ exist?' /
'where is symbol X?'. Add two jailed, gitignore-aware read-only tools:

- GlobTool (name 'glob', T1, FILE_READ+DIRECTORY_LIST): find files by
  glob pattern; survey-exempt from anti-hallucination read gates like
  list_dir.
- GrepTool (name 'grep', T1, FILE_READ): regex content search, returns
  path:line: text; skips gitignored, binary (NUL), and >2MB files.

Both reuse GitignoreMatcher + PathJail from the filesystem package,
share FileReadTool's jail/anchor/toggle, cap at 200 results. Registered
in ToolConfig.buildTools (fileRead block) and added to
StageConfig.ALWAYS_AVAILABLE_READ_TOOLS so every tool-granting stage can
call them. 6 tests green.

Vikunja #37.

core/transitions/src/main/kotlin/com/correx/core/transitions/graph/StageConfig.kt

@@ -66,6 +66,6 @@ data class StageConfig(
 
     companion object {
         /** Read-only tools every tool-granting stage may call regardless of its declared set. */
-        val ALWAYS_AVAILABLE_READ_TOOLS: Set<String> = setOf("file_read", "list_dir")
+        val ALWAYS_AVAILABLE_READ_TOOLS: Set<String> = setOf("file_read", "list_dir", "glob", "grep")
     }
 }