Show plugin names in file opener menus - #5241

Human comments

What was wrong

File opener labels used internal plugin IDs or generic titles, making installed plugins such as Docs difficult to identify.

What changed

• File opener settings and both file-link menus show plugin names, such as “Docs (Markdown).”
• Automatic selections identify the plugin while saved preferences keep their existing IDs.
• When an opener's title repeats its plugin name (the bundled File Editor), the name shows once.

How you verified

• Chrome for Testing 155 (headless) on isolated QA builds of 599c051 and 74ba862 with the bundled Docs and File Editor plugins: Settings → Files dropdowns (.md, .ts) at 1440×900 and 390×844, the thread file-link context menu, and the Docs file-link “Open with” submenu show plugin names; File Editor shows once (no “File Editor (File Editor)”).
• Selecting “Docs (Markdown)” for .md stored {"md":"simple-notes:docs"} and stayed selected after a hard reload; no console errors.
• Remote CI passed on 74ba862, including a regression test for the repeated-name label.
• Slop Cop on f411b13 (rebased head): one P1, the doubled "File Editor (File Editor)" label, fixed in 74ba862. No other P0/P1.

Follow-ups (P2, not in this PR):

• Add label tests for the two file-link menus, which only the settings test covers today.
• "Automatic (Docs)" doesn't name the opener when one plugin registers several for an extension.
• The SDK doc for a file opener's title still calls it the "Open with" label; it is now a qualifier after the plugin name.

User QA pending.

Before: 599c051 · After: 74ba862 · Captured at 2×

Screen / state	Viewport	Before	After
Settings → File openers / .md dropdown open	Desktop · 1440×900
Settings → File openers / .ts dropdown open	Desktop · 1440×900
Settings → File openers / .md dropdown open	Mobile · 390×844
Settings → File openers / .ts dropdown open	Mobile · 390×844
Docs file link / Open with submenu	Desktop · 1440×900
Thread message .md link / context menu	Desktop · 1440×900
Thread message .ts link / context menu	Desktop · 1440×900

BB-Thread-ID: thr_kfd893acyi

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