feat: post-processing profiles with their own shortcuts

[VitoMakarevich]

Before Submitting This PR

Please confirm you have done the following:

• I have searched existing issues and pull requests (including closed ones) to ensure this isn't a duplicate
• I have read CONTRIBUTING.md

If this is a feature or change that was previously closed/rejected:

• I have explained in the description below why this should be reconsidered
• I have gathered community feedback (link to discussion below)

Human Written Description

Adds post-processing profiles: add/delete/update profiles, each identical to what was there before (keybinding / backend / prompts) — no changes to how post-processing itself works. The name of the profile being used is shown while post-processing, all new text is localized, and retrying a history entry falls back to no post-processing if its profile was deleted.

Profiles are managed with a tabs interface on the Post Processing page: + adds a tab, × deletes it, and double-clicking a tab title renames it.

So the process of using multiple profiles is:

1. Set up multiple profiles (e.g. one for local inference, and as many custom others as you wish).
2. Assign a separate keybinding to each.

E.g. I use one for local qwen, one for gpt-6-luna and one for gpt-6-sol, and assign F5/F6/F7 to them.

Why this should be reconsidered

TODO (author): similar requests were closed before (#334, #1606, see below). Explain in your own words why this should be reconsidered and link the discussion with community support.

Migration

The current setup moves into an undeletable Default profile:

• Settings (schema 2 → 3): the old flat post_process_* settings (provider, base URL, API keys, models, prompts, selected prompt) become the Default profile, which keeps the existing "Transcribe with post-processing" shortcut, so nothing needs reconfiguring. --toggle-post-process and SIGUSR1 trigger Default.
• History (migration 5): adds post_process_profile_id; existing post-processed entries are assigned to Default. Deleting a profile clears the id on its entries (app-level ON DELETE SET NULL, since profiles live in the settings store), and retrying such an entry skips post-processing instead of sending it to another provider.

Related Issues/Discussions

Previously closed:

• ✨ Feature Request: Separate Shortcuts for Raw Transcription vs Post-Processing + Selectable Post-Processing Profiles #334 — Feature request: separate shortcuts for raw vs post-processed transcription + selectable post-processing profiles (closed as not planned; redirected to Discussions).
• feat: add prompt picker hotkey for post-processing #1606 — PR: prompt picker hotkey for post-processing (closed under the feature freeze). Same need, different design: one hotkey + a modal to choose a prompt, versus one shortcut per profile here.

Related discussions:

• Transcript post-processing #168 — Transcript post-processing
• Have ideas for a shortcut?! Post here! #211 — Have ideas for a shortcut?! Post here!
• Improve Multilingual Dictation UX with Profiles and Quick Profile Switching #1534 — Improve Multilingual Dictation UX with Profiles and Quick Profile Switching

Discussion: TODO (author): link the discussion with community support.

Community Feedback

TODO (author): link community feedback.

Testing

• cargo test: 290 passing, including new tests for the settings migration, profile add/rename/delete invariants, recovery from a malformed profile, profile resolution by shortcut, the history migration backfill, ON DELETE SET NULL, and retry routing.
• tsc, eslint, check:translations (all locales), prettier / cargo fmt clean.
• Manually on macOS (Apple silicon) with an existing 0.9.x settings store: the Default profile kept the Custom provider, base URL, model, prompts, API keys and shortcut; three profiles on F5/F6/F7 each post-processed with their own provider/model (confirmed in the logs); settings and history migrations verified on real data.
• Not tested on Windows or Linux.

Screenshots/Videos (if applicable)

TODO (author): screenshot of the profile tabs.

AI Assistance

• No AI was used in this PR
• AI was used (please describe below)

If AI was used:

• Tools used: Claude Code
• How extensively: Implementation, tests and translations written with Claude Code, following my spec and review; I tested the feature by hand.