feat(guardrails): steering channel + shell-in-file rule + capability-gap detector

Bundles three operator-reliability guardrails (Vikunja #28/#29/#30) plus the
in-flight branch WIP they were built on top of (reasoning_content capture,
operator/project profile editor, write-jail workspaceRoot fix) — the tree is
interdependent (SessionOrchestrator references reasoningArtifactId from the WIP)
and does not compile as separable subsets, so it lands as one commit.

Guardrails:
- #28 mid-stage steering: ClientMessage.SteerSession -> GlobalStreamHandler ->
  orchestrator.submitSteering, reusing SteeringNoteAddedEvent + existing context
  fold (advisory, non-authoritative; invariants #3/#7). Closes the gap where
  steering typed off an approval gate was silently dropped.
- #29 shell-in-file guardrail: ShellInFileContentRule (core:toolintent) blocks a
  file_write whose content is a bare shell command (e.g. "mkdir -p ..."); FileWriteTool
  description now advertises auto-mkdir of parent dirs. Basename-allowlist so the
  extensionless case is caught; scripts/Makefiles/multiline exempt.
- #30 pt1 capability-gap detector: deterministic CapabilityGapDetector maps stage
  intent -> implied ToolCapability, compares to granted tools, emits advisory
  CapabilityGapDetectedEvent in FreestyleDriver.lockAndRun. Recorded, never fails
  the gate and never auto-grants (invariants #3/#4/#5). Reflection rung is pt2.

Verified: ./gradlew check green (whole tree).

examples/workflows/freestyle_planning.toml

@@ -1,5 +1,16 @@
 id = "freestyle_planning"
-start = "analyst"
+start = "discovery"
+
+# discovery runs before the analyst: it vets the request against the real repo and either clears
+# it to plan or parks on a batched list of operator questions (grounds contradictions too, e.g. a
+# request naming an endpoint the server doesn't expose). Read-only; owns clarification exclusively.
+[[stages]]
+id = "discovery"
+prompt = "prompts/discovery.md"
+produces = [{ name = "discovery", kind = "discovery" }]
+allowed_tools = ["file_read", "list_dir", "shell"]
+token_budget = 16384
+max_retries = 2
 
 # analyst writes no files, but it owns task framing: task_search/task_context (read-only) find
 # existing work; task_create (T2, approval-gated — a task is an event-log entry, not a file write)
@@ -24,6 +35,13 @@ produces = [{ name = "execution_plan", kind = "execution_plan" }]
 token_budget = 16384
 max_retries = 2
 
+[[transitions]]
+id = "discovery-to-analyst"
+from = "discovery"
+to = "analyst"
+condition_type = "artifact_validated"
+condition_artifact_id = "discovery"
+
 [[transitions]]
 id = "analyst-to-architect"
 from = "analyst"