feat(mcp): add multi-account profile support

[JSONbored]

Parent roadmap: #82

Background

Some users maintain multiple GitHub identities. Gittensory must not mix sessions, evidence, or local config across identities.

Goal

Support named local MCP profiles for multiple GitHub/Gittensory sessions.

Current Behavior

Local config supports auth, but multi-account profile handling is not a first-class workflow.

Desired Behavior

Users can create, list, switch, and remove profiles without token leakage or evidence mixing.

Implementation Requirements

• Add profile-aware config storage.
• Update login/logout/whoami/status/doctor.
• Keep default profile simple for normal users.
• Avoid printing token paths or secrets.
• Make API requests include the selected session only.

Public/Private Output Boundaries

MCP may return private scoreability and risk context to authenticated users. It must never upload source contents by default, and public-safe packet output must exclude private score/reward/trust/reviewability details.

Acceptance Criteria

• whoami reflects active profile.
• Switching profiles changes session safely.
• Logout only affects selected profile unless requested.
• Doctor reports profile state without leaking secrets.

Testing Requirements

• npm run test:ci must pass.
• Global coverage must remain at or above 97% for lines, statements, functions, and branches.
• Aim for 98%+ branch coverage locally to avoid CI variance.
• Add tests for every new branch, fallback path, sanitizer rule, and regression.
• Add invariant/property-style tests when behavior depends on sorting, gating, scoring, queue pressure, source-upload safety, public/private boundaries, or upstream drift.
• Public GitHub output must be tested against forbidden language: wallet, hotkey, raw trust score, payout, reward estimate, farming, private reviewability, and public score estimate.
• MCP/local tooling must prove source contents are not uploaded.

Additional Test Scenarios

• Two-profile fixture.
• Logout selected profile.
• Missing profile fallback.
• Token redaction regression.