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).

core/config/src/main/kotlin/com/correx/core/config/OperatorProfileWriter.kt

@@ -0,0 +1,48 @@
+package com.correx.core.config
+
+import java.nio.file.Files
+
+/**
+ * Serializes an [OperatorProfile] back to TOML text that [ProfileLoader] reads identically,
+ * mirroring [ProjectProfileWriter]'s regenerate-the-file, skip-empty-sections approach.
+ */
+object OperatorProfileWriter {
+
+    /** Renders [profile] as TOML. String values escape `\` and `"`; empty sections are skipped. */
+    fun serialize(profile: OperatorProfile): String {
+        val b = StringBuilder()
+
+        if (profile.about.isNotBlank()) {
+            b.append("about = ").append(str(profile.about)).append('\n')
+        }
+
+        val prefs = profile.preferences
+        val hasPrefs = prefs.approvalMode.isNotBlank() || prefs.preferredModels.isNotEmpty() || prefs.conventions.isNotEmpty()
+        if (hasPrefs) {
+            if (b.isNotEmpty()) b.append('\n')
+            b.append("[preferences]\n")
+            if (prefs.approvalMode.isNotBlank()) {
+                b.append("approval_mode = ").append(str(prefs.approvalMode)).append('\n')
+            }
+            if (prefs.preferredModels.isNotEmpty()) {
+                b.append("preferred_models = ").append(list(prefs.preferredModels)).append('\n')
+            }
+            if (prefs.conventions.isNotEmpty()) {
+                b.append("conventions = ").append(list(prefs.conventions)).append('\n')
+            }
+        }
+
+        return b.toString()
+    }
+
+    /** Writes [profile] to `<homeDir>/.config/correx/profile.toml`, creating parent dirs if missing. */
+    fun write(profile: OperatorProfile, homeDir: String = System.getProperty("user.home")) {
+        val path = ProfileLoader.profilePath(homeDir)
+        Files.createDirectories(path.parent)
+        Files.writeString(path, serialize(profile))
+    }
+
+    private fun str(v: String): String = "\"" + v.replace("\\", "\\\\").replace("\"", "\\\"") + "\""
+
+    private fun list(v: List<String>): String = "[" + v.joinToString(", ") { str(it) } + "]"
+}