fix: chore(26a): delete action-agent.sh, action-poll.sh, and action/AGENTS.md (#65)

- Delete action/ directory and all its contents
- Remove action-bot from bin/disinto bot token mapping and collaborator lists
- Remove FORGE_ACTION_TOKEN from lib/env.sh and .env.example
- Remove action-bot from FORGE_BOT_USERNAMES in lib/env.sh and .env.example
- Update .woodpecker/agent-smoke.sh to remove action script checks
- Update AGENTS.md: remove action agent from description and table
- Update lib/AGENTS.md: remove action-agent references from sourced by columns
- Update docs/PHASE-PROTOCOL.md: remove action-agent reference
- Update docs/AGENT-DESIGN.md: remove action-agent from agent table
- Update planner/AGENTS.md: update action formula execution reference
- Update README.md: update formula-driven execution reference

Part of #26 — retire action-agent system.

.env.example

@@ -26,8 +26,7 @@ FORGE_GARDENER_TOKEN=                      # [SECRET] gardener-bot API token
 FORGE_VAULT_TOKEN=                         # [SECRET] vault-bot API token
 FORGE_SUPERVISOR_TOKEN=                    # [SECRET] supervisor-bot API token
 FORGE_PREDICTOR_TOKEN=                     # [SECRET] predictor-bot API token
-FORGE_ACTION_TOKEN=                        # [SECRET] action-bot API token
-FORGE_BOT_USERNAMES=dev-bot,review-bot,planner-bot,gardener-bot,vault-bot,supervisor-bot,predictor-bot,action-bot
+FORGE_BOT_USERNAMES=dev-bot,review-bot,planner-bot,gardener-bot,vault-bot,supervisor-bot,predictor-bot
 
 # ── Backwards compatibility ───────────────────────────────────────────────
 # If CODEBERG_TOKEN is set but FORGE_TOKEN is not, env.sh falls back to