🔧 Add AGENTS.md and CLAUDE.md, remove copilot-instructions

Consolidate agent instructions into AGENTS.md with commands, architecture,
design constraints, protocols, pitfalls, and commit/PR conventions.
CLAUDE.md is a symlink to AGENTS.md. Copilot instructions removed as all
content is now covered by AGENTS.md.

Co-Authored-By: OpenCode <noreply@opencode.ai>

Author: 0x46616c6b

.github/copilot-instructions.md

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+# Agent Instructions
+
+## Commands
+
+```bash
+go test ./...                 # run all tests
+golangci-lint run             # lint (CI uses golangci-lint-action)
+mockery                       # regenerate mocks (committed as mock_UserliService.go)
+```
+
+CI runs: lint → test (with coverage) → goreleaser snapshot build. No required local order.
+
+## Architecture
+
+Single-package `main` app — all `.go` files live in the repo root, no `cmd/` or `internal/`.
+
+Key abstraction: `ConnectionHandler` interface in `tcpserver.go` — both `LookupServer` and `PolicyServer` implement it; `StartTCPServer()` provides shared connection pooling, graceful shutdown, and metrics.
+
+## Design Constraints
+
+- **Fail-open**: API errors must return `DUNNO`/allow and never block mail delivery
+- **No PII in metrics**: aggregate counters only, no email addresses in Prometheus labels
+- Never store `context.Context` in structs — pass through function parameters
+
+## Protocols
+
+Socketmap (lookup): netstring-encoded `<len>:<mapname> <key>,` → `<len>:<status> <data>,`
+Responses: `OK <data>`, `NOTFOUND`, `TEMP <msg>`, `PERM <msg>`
+
+Policy delegation: `name=value\n` pairs, empty line terminates → `action=ACTION\n\n`
+Only process at `protocol_state=END-OF-MESSAGE` for accurate counting.
+
+## Pitfalls
+
+- `USERLI_TOKEN` is required — app exits immediately if missing
+- Rate limiter cleanup runs every 5 minutes in a background goroutine
+- Socketmap names must match exactly: `alias`, `domain`, `mailbox`, `senders`
+
+## Docker Development
+
+```bash
+cp .env.example .env
+docker compose up
+docker compose exec userli bin/console doctrine:schema:create
+docker compose exec userli bin/console doctrine:fixtures:load --no-debug
+```
+
+Fixtures must be loaded manually after first start.
+
+## Commits
+
+- **Gitmoji** style: e.g., `:sparkles: Add feature`, `:bug: Fix rate limiter`, `:recycle: Refactor server`
+- Add `Co-Authored-By: OpenCode <noreply@opencode.ai>` to the commit message
+
+## Pull Requests
+
+- Open as **draft**
+- Write description in English
+- Label PRs for release-drafter:
+  - `feature` (major), `enhancement` (minor)
+  - `fix` / `bugfix` / `bug` (patch)
+  - `chore` / `dependencies` (patch, maintenance)

AGENTS.md

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+AGENTS.md