fix(agents): list Implementer/Verifier in agent_spawn + agent_assign schemas (#404)

The SubAgentType enum gained `Implementer` and `Verifier` variants in #404,
but the JSON-schema `description` strings on AgentSpawnTool::input_schema
and DelegateToAgentTool::input_schema still listed the pre-#404 set
(general/explore/plan/review/custom). The model only sees those
descriptions, so the new roles were effectively hidden behind a
docs lookup.

Updates both descriptions to the post-#404 surface and references
docs/SUBAGENTS.md for posture. Also adds the long-form aliases
(builder/validator/tester) to the agent_assign hint so it matches
the canonical alias map. Pure copy change — no behaviour delta.

CHANGELOG.md

@@ -110,6 +110,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **Sub-agent description copy** — `agent_spawn` tool description
   and `prompts/base.md` updated to reflect the new default cap of
   10 (was stale "Max 5 in flight").
+- **`agent_spawn` / `agent_assign` schema descriptions** (#404
+  follow-up) — type/agent_name property descriptions now list
+  `implementer` and `verifier` so the model surfaces those roles
+  without having to discover them from `docs/SUBAGENTS.md`. Adds
+  the long-form aliases (`builder` / `validator` / `tester`) on
+  `agent_assign` for parity with the alias map.
 - **RLM tool family** (#512) — `rlm` tool cards map to
   `ToolFamily::Rlm` and render `rlm`, not `swarm`. Stale "swarm"
   wording cleaned out of docs / comments / tests.

crates/tui/src/tools/subagent/mod.rs

@@ -1467,7 +1467,7 @@ impl ToolSpec for AgentSpawnTool {
                 },
                 "type": {
                     "type": "string",
-                    "description": "Sub-agent type: general, explore, plan, review, custom"
+                    "description": "Sub-agent type: general, explore, plan, review, implementer, verifier, custom. See docs/SUBAGENTS.md for posture per role."
                 },
                 "agent_type": {
                     "type": "string",
@@ -2325,7 +2325,7 @@ impl ToolSpec for DelegateToAgentTool {
             "properties": {
                 "agent_name": {
                     "type": "string",
-                    "description": "Name/type alias for the agent (general, explore, plan, review, worker, explorer, awaiter)"
+                    "description": "Name/type alias for the agent (general, explore, plan, review, implementer, verifier, worker, explorer, awaiter, builder, validator, tester)"
                 },
                 "type": {
                     "type": "string",