feat: dual execution model (SSH CLI + HTTP pull)

- ExecutionMode enum: SshCli (orchestrator dispatches) | HttpPull (agent pulls)
- SSH CLI executor: spawn remote agents via ssh + CLI template
- Local subprocess as SSH special case (localhost)
- HostConfig with capability matching and load-based selection
- Dispatch loop: scan created tasks → select host → execute → update
- CliAdapterConfig: CLI templates for Codex and Claude Code
- Structured prompt construction (Issue → goal/constraints/validation)
- Output parsers: Codex JSON, Claude Code JSON, raw fallback
- TaskStatus::ReviewPending + review_count loop limit
- Forgejo webhook: pull_request (opened→review_pending, merged→completed)
- Forgejo webhook: push events (task/* branch → last_activity_at)
- HTTP API: dequeue only returns http_pull tasks
- HTTP API: status update only for http_pull mode
- Token auth config for http_pull agents
- Adapter module rewritten: AgentAdapter trait removed → config-driven CLI templates
- New fields: execution_mode, assigned_host, branch_name, pr_title, last_activity_at, review_count
- 30/30 tests pass

openspec/changes/dual-execution-model/specs/notification-via-forgejo/spec.md

@@ -0,0 +1,33 @@
+## MODIFIED Requirements
+
+### Requirement: Git branch as task execution unit
+每个任务 SHALL 关联一个 Git 分支，无论哪种执行模式。Agent 在该分支上工作，通过 PR 提交结果。
+
+#### Scenario: ssh_cli mode — Orchestrator creates branch
+- **WHEN** ssh_cli 模式任务开始执行
+- **THEN** Orchestrator SHALL 在目标仓库创建分支 `task/{task_id}`（通过 SSH 在远程主机执行 `git checkout -b`）
+- **AND** 将分支名传入 Agent prompt
+
+#### Scenario: http_pull mode — Agent creates branch
+- **WHEN** http_pull 模式任务被 Agent 领取
+- **THEN** Agent SHALL 自行创建分支 `task/{task_id}`
+
+### Requirement: PR webhook as completion notification
+无论哪种执行模式，Agent 完成任务后 SHALL 通过 Forgejo PR 触发状态更新。
+
+#### Scenario: ssh_cli mode — Agent creates PR via CLI
+- **WHEN** ssh_cli 模式的 Agent 执行完成
+- **THEN** Agent（或 Orchestrator 通过 SSH） SHALL push 到 task 分支并创建 PR
+- **AND** Forgejo PR webhook 触发状态更新
+
+#### Scenario: http_pull mode — same flow
+- **WHEN** http_pull 模式的 Agent 执行完成
+- **THEN** Agent SHALL push 到 task 分支并创建 PR
+- **AND** Forgejo PR webhook 触发状态更新（与 ssh_cli 模式相同）
+
+### Requirement: Push events as progress tracking
+无论哪种执行模式，Forgejo push webhook SHALL 作为进度信号。
+
+#### Scenario: ssh_cli mode — push detected
+- **WHEN** ssh_cli 模式执行中，Agent push 到 task 分支
+- **THEN** Orchestrator 更新 `last_activity_at`（与 http_pull 模式相同）