feat: per-workspace override for the workspace memory char limit

feat: per-workspace override for the workspace memory char limit

Feature description

The workspace memory character limit is a single global admin setting. Larger
or smaller workspaces may warrant different memory budgets, but the global
value applies everywhere.

Proposed solution

Allow admins to override the workspace memory char limit per workspace from
the Memory settings UI:

• Overrides stored as a path-keyed map in the existing config table (e.g. memory.workspace_char_limit_overrides).
• Resolved inside get_memory_settings(), so writes, recall budgets, and background review all honor the override with no other changes.
• PUT /api/memory/config accepts a workspace and routes the workspace limit into the override map; clearing it falls back to the global value.
• Memory settings UI shows a workspace limit input when a workspace is active.
• Clamp/validate override values; handle invalid input gracefully.

Additional context

Implemented on a fork, including tests (override resolution, clamping, invalid values, clearing, batch-write enforcement).

Start by locating get_memory_settings(), the PUT /api/memory/config handler, the existing config table, and the Memory settings UI. Trace how the global limit reaches writes, recall budgets, and background review, then verify workspace overrides, clamping, invalid-input handling, clearing, and batch-write enforcement with the fork's referenced tests.