[app-bug] No /settings page — users can't configure analyzer path, custom rules, AI provider

[Gbangbolaoluwagbemiga]

Problem

The CLI and API both honour env vars (SANCTIFIER_BIN, AI_EXPLAIN_PROVIDER, custom rules paths). The web UI has no way to set or even view these — every user has to read the README and shell-export.

Acceptance Criteria

• New /settings route with tabs: Analyzer, AI, Theme, Telemetry
• Analyzer tab: binary path (free text), .sanctify.toml override (free text), custom-rules YAML upload
• AI tab: provider selector (stub / Anthropic / OpenAI / local), API key field (masked), daily cost cap
• All settings persisted to localStorage and forwarded to /api/analyze and /api/ai/explain via headers
• A11y: real <form>, real labels, keyboard reachable

Pointers

• frontend/app/api/analyze/route.ts
• frontend/app/api/ai/explain/route.ts

Difficulty

Medium. UI + persistence + header plumbing.