feat: fold bot-bottle-orchestrator into bot_bottle/orchestrator subpackage

Moves the orchestrator into bot_bottle/orchestrator/ so one install gets
everything. Entry point is now `python -m bot_bottle.orchestrator run`.

- Add bot_bottle/orchestrator/ with all 14 modules (verbatim move; internal
  imports were already relative, so no changes inside orchestrator modules)
- Rewrite bootstrap.py: remove the lazy bot_bottle import guard, use direct
  relative imports from ..contrib.*
- Add bot_bottle/contrib/forge/base.py: ScopedForge (read-anywhere / write-scoped)
- Add bot_bottle/contrib/gitea/client.py: GiteaClient + GiteaForge (urllib.request only)
- Add bot_bottle/contrib/gitea/forge_state.py: ForgeState + SqliteForgeStateStore
- Add tests/unit/orchestrator/ (82 tests: 63 migrated + 19 new for contrib modules)

Closes #321

bot_bottle/contrib/forge/base.py

@@ -0,0 +1,52 @@
+"""Scoped forge wrapper: read-anywhere / write-scoped access control.
+
+`ScopedForge` wraps any forge object and restricts write operations to
+the set of issue/PR numbers the agent is explicitly assigned to. Read
+operations always pass through unconditionally.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+
+class ScopedForge:
+    """Delegates all forge calls to an inner forge, raising `PermissionError`
+    on write calls for numbers outside the assigned scope."""
+
+    def __init__(
+        self,
+        forge: Any,
+        *,
+        assigned_issue: int,
+        assigned_prs: list[int],
+    ) -> None:
+        self._forge = forge
+        self._allowed_writes: frozenset[int] = frozenset({assigned_issue, *assigned_prs})
+
+    def _check_write(self, number: int) -> None:
+        if number not in self._allowed_writes:
+            raise PermissionError(
+                f"write to #{number} is outside the assigned scope "
+                f"(allowed: {sorted(self._allowed_writes)})"
+            )
+
+    def is_org_member(self, org: str, username: str) -> bool:
+        return self._forge.is_org_member(org, username)
+
+    def read_issue(self, number: int) -> dict[str, Any]:
+        return self._forge.read_issue(number)
+
+    def read_pr(self, number: int) -> dict[str, Any]:
+        return self._forge.read_pr(number)
+
+    def read_comments(self, number: int) -> list[dict[str, Any]]:
+        return self._forge.read_comments(number)
+
+    def post_comment(self, number: int, body: str) -> None:
+        self._check_write(number)
+        self._forge.post_comment(number, body)
+
+    def update_description(self, number: int, body: str) -> None:
+        self._check_write(number)
+        self._forge.update_description(number, body)