Clarify dependency removal PR policy in AGENTS.md (#228)

## Summary
Updated the dependency management guidance in AGENTS.md to explicitly
clarify that removing dependencies requires a dedicated PR, even when
the removal is paired with deleting the code that used the dependency.

## Changes
- Expanded the dependency change policy to explicitly mention "remove"
alongside "add" and "bump"
- Added clarification that dependency removals rewrite `uv.lock` and
therefore warrant their own PR to avoid merge conflicts with feature
branches
- Emphasized that this applies even when a dependency removal is coupled
with deleting the code that depended on it

## Rationale
The original guidance only mentioned adding or bumping dependencies as
requiring dedicated PRs. This update makes explicit that the same
principle applies to removals, since `uv.lock` changes are the root
cause of merge conflicts — not the semantic nature of the change. This
prevents feature branches from colliding in the lockfile when one
removes a dependency and another adds one.

https://claude.ai/code/session_01BBoBygev93Rkj1AcowNsjA

Co-authored-by: Claude <noreply@anthropic.com>

Author: alexkroman

AGENTS.md

@@ -59,9 +59,10 @@ structured so independent changes stay in disjoint files. Keep it that way:
   declaration (see `aai_cli/AGENTS.md`). If you find yourself editing a shared
   list to add a command, you're fighting the convention.
 - **Dependency changes are not part of feature PRs.** `uv.lock` is the one file
-  two branches can never merge cleanly; add or bump dependencies in a
+  two branches can never merge cleanly; add, bump, or remove dependencies in a
   dedicated, single-purpose PR so feature branches don't collide in the
-  lockfile.
+  lockfile. Dropping a dependency still rewrites `uv.lock`, so a removal gets
+  its own PR too — even when it rides along with deleting the code that used it.
 - **Land through the merge queue.** The diff-scoped gates compare against
   `origin/main`, which moves constantly; two individually-green PRs can be
   jointly red. PRs should merge via GitHub's merge queue (a repository setting)