feat(plugin): ship the agents from a single root agents/ directory

Move .claude/agents/ and server/data/agent-templates/ship-feature-lane/
into one agents/ at the repo root — which IS the plugin root, so all five
agents now ship with the ccam plugin as ccam:<name>, the same way skills
already do.

The two pipeline agents were byte-identical copies in both places; that
duplication is gone. `ccam lanes agents install` now reads them straight
from agents/, so the per-lane copy in <lane>/.claude/agents/ still gives
the bare `subagent_type: qc-local` the ship-feature-lane skill prefers.
Skill and docs record both names: bare inside a lane, ccam: as fallback.

SETUP.md

@@ -169,7 +169,7 @@ This repository ships extension files for both agent ecosystems:
   - `CLAUDE.md`
   - `.claude/rules/*`
   - `skills/*` (the `ccam` plugin's own skills)
-  - `.claude/agents/*`
+  - `agents/*` (the `ccam` plugin's own agents)
 - Codex:
   - `AGENTS.md`
   - `.codex/config.toml`