feat(mecatui): own configurable terminal titles

[jbeda]

Implementation

Implements the approved terminal-title contract from Plan / Interface PR #1616.

Delivered

• Mecatui owns title rendering and emits deduplicated OSC 0 updates for both terminal icon/tab and window-title surfaces instead of Bubble Tea OSC 2 output.
• Adds strict user-global terminal_title.enabled and terminal_title.template settings over safe plain-text status facts, plus display-width elide.
• Preserves explicit --terminal-title and MECATUI_NO_TERMINAL_TITLE precedence and conditional cleanup.
• Removes session handles from default header/title presentation, preserves opt-in template access, and enables read-only /session details during active runs.
• Keeps ordinary session handles terminal-safe and copy/paste-safe under ADR 0285: non-safe ID bytes are percent-encoded into fixed short handles; debug resolves only canonical handle operands locally and sends exact IDs to the server.
• Excludes private workspace paths and StatusML helpers from title templates; includes race, configuration, terminal-control, and live-run regressions.

Plan / Interface PR: #1616
Approved baseline: 2a0c9cb11bedc6ef88503f504bbd4f94a6d31690
Interfaces match approved contract: Yes

Validation

• task lint
• task test
• task e2e:k8s
• task ac-trace-strict
• task docs
• task site:build
• git diff --check

Fixes #1460.

Related: #1606.