Consolidate reviewed session interop, pagination, and repeated-turn fixes

[cuevasclemente]

Summary

Consolidate the reviewed production-ready Wayang work that had accumulated on local canonical main after PR #42:

• reviewed Qwen model-picker resolution;
• bounded Standard-session transcript/attachment interop and its audit hardening;
• long-session window-v1 transcript pagination;
• repeated-user-turn deduplication integrated with pagination, queued turns, optimistic echoes, session selection, and streaming snapshots.

The repeated-turn cherry-pick initially exposed pagination-specific races. The integration now admits windows before side effects, treats only new tail-authoritative occurrences as acceptance, rejects ID-less window-mode user replays, activates exact correlation at protocol negotiation, and preserves assistant snapshot ordering. Three independent review passes ended in GO.

Validation

• backend release suite: 1017 passed, 6 skipped, 0 failed;
• frontend tests: 4/4;
• frontend lint: 0 errors, one pre-existing Fast Refresh warning;
• frontend production build: pass;
• focused transcript/queue/pagination matrix: 31/31;
• full Playwright suite: 113/113;
• git diff --check: pass;
• make check reaches the unchanged synthetic Bitwarden-helper baseline failure: 62/63 script tests, with all preceding gates passing.

Deliberately excluded

• draft PR Make historical agent authority deployment-bound #35 (feat/generic-capabilities), which retains a documented authority-lifecycle NO-GO;
• the 18k-line Android M0-M4 stack, which requires its own current review/PR;
• appearance/font WIP, audio experiment preservation refs, backup/rescue branches, and dirty worktrees.

No service restart or host deployment is part of this PR.