fix(server): warn when a recorded flow backtracks

[kushals256]

Summary

• A recorded drive that clicks into a product and then "back" to search saved both clicks and dropped the navigation between them. Replay landed on the product page and looked for a search-only control.
• reticle_record stop and reticle_flow_save now warn when the recorded route list returns to an earlier page (/search → /product/1 → /search). Linear A→B→C stays quiet; consecutive stays on the same page are collapsed so a re-render is not a backtrack.
• The flow-file format is unchanged. The route list is in-memory only and is not written to disk.

Fixes #603.

Test plan

• recording-backtrack.test.ts — silent on linear/single-page, warns on return, hash-router pages are distinct, to fallback
• record-stop-backtrack.test.ts — stop warns on a backtracking window, quiet on linear
• flow-save-recording.test.ts — save warns, does not persist routes, linear stays quiet
• existing record-stop-budget / flow-save tests stay green

Made with Cursor

[kushals256]

Same coverage-floor flake as #750 / #753 / #755 / #757, not this change. This run shrank 48 → 45: hidden-api-500 timed out on MCP initialize for Playwright and DevTools, and broken-form-validation/playwright hung on browser_click. Catch-rate stayed 1.0.

Cherry-picked the one-retry from #750 (the same rule replay-detect already uses for a flaky baseline). A missing tool is still a miss.