Rename MCP skills to toolsets and support finer-grained tool access controls

## Summary
Rename the current skill-based MCP authorization/tool exposure model to "toolsets" and extend it with more granular controls for which tools are exposed.

## Evidence
- The repository currently presents MCP capability groups as "skills" in code, docs, CLI flags, environment variables, and the OAuth approval UI.
- `packages/mcp-core/src/skills.ts` defines the current skill registry: `inspect`, `seer`, `docs`, `triage`, and `project-management`.
- `packages/mcp-core/src/server.ts` filters registered tools from `context.grantedSkills`.
- The stdio transport supports coarse controls via `--skills`, `MCP_SKILLS`, `--disable-skills`, and `MCP_DISABLE_SKILLS`.
- The remote OAuth approval dialog renders selectable skills from `skillDefinitions`.
- Validation performed: inspected the current skills implementation, docs, CLI configuration, OAuth approval UI, and duplicate-search candidates. No runtime tests were run because this is a feature/design request.

## Impact
Users and maintainers who configure MCP permissions currently interact with "skills" terminology and coarse-grained bundles. Renaming them to "toolsets" may better match common MCP terminology, while finer-grained controls could reduce unnecessary tool exposure and token overhead.

## Next Steps
- Decide the desired public terminology and migration path from "skills" to "toolsets".
- Define the granularity model: named toolsets only, per-tool allow/deny lists, or both.
- Update core types, generated definitions, OAuth approval UI, stdio flags/env vars, docs, and tests consistently.
- Preserve backward compatibility for existing `skills`/`grantedSkills` tokens or configuration where needed.

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## Original Report

Original issue text

### Original Title

Rename skill-based permissions to toolsets and add more granular controls

### Original Body

_No body provided._