fix(mobile): keep the dictation timer from shifting width

[juliusmarminge]

The dictation timer changed width as its digits ticked, both in the composer and in the edge pill from #15502. Its fontVariant: ["tabular-nums"] did nothing: the app font, DM Sans, has no tnum feature, and its digits range from 312 units wide ("1") to 684 ("0").

The timer now renders in the system font, which honors tabular-nums, the same approach the floating "Working" timer already uses. Both timers share one DictationElapsedTime component.

Verification: mobile typecheck passes, voice-input tests pass (31), targeted lint is clean.

Model: Claude Opus 5.5. Harness: Claude Code in T3 Code.

🤖 Generated with Claude Code

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[macroscopeapp]

Approvability

Verdict: Approved at 8a7fd9c

Macroscope's review found this PR approvable — This is a contained mobile UI bug fix that preserves dictation behavior while replacing duplicated timer rendering with a system-font component that keeps tabular digits from changing width. Its runtime impact is limited to the existing recording timer displays, with no product-default, static-analysis, schema, or workflow changes.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	4.9 KiB	4.9 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.7 KiB	3.7 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.4 KiB	20.4 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	4.9 KiB	4.9 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.7 KiB	3.7 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	20.8 KiB	20.8 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: daa1d0e · PR result: 8a7fd9c · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 106.1 KiB
• Claude decoded thread snapshot: 106.4 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.