fix: prevent futile retries after empty or deferred results

[jlitola]

Summary

• replace empty search and grep dead ends with compact, bounded next actions and explicit unchanged-retry prevention
• expose bounded search-status waiting through MCP wait_timeout_ms and CLI --wait, defaulting to 20 seconds
• stop FAILED and TIMEOUT session polling consistently across text, JSON, MCP, and CLI
• preserve backend indexing, not-found, freshness, filter, estimate, and alternative-target diagnostics across MCP and CLI output
• humanize real producer-normalized grep truncation reasons and keep surface-specific recovery syntax accurate
• document the public text-v1 behavior and MCP/CLI parity contract

Release follow-up (required)

This PR deliberately does not bump package versions. A separate release PR must bump both the root githits package and @githits/mcp; the MCP package must move off the already-published 0.6.4 or the MCP release workflow will skip publishing these changes. After publication, the hosted remote MCP must consume the new @githits/mcp version and be redeployed before remote users receive the new guidance and search_status.wait_timeout_ms behavior.

Validation

• bun test: 2627 passed
• bun run typecheck
• bun run format:check
• bun run lint
• bun run build
• bun run smoke:cli authenticated
• bun run smoke:mcp authenticated
• targeted Claude and Codex agent E2E workloads for unified search; both succeeded with high confidence and reported GitHits helped
• GitHub CI, MCP package validation, and runtime compatibility matrix pass