Add adjustable conversation message text size

[torlando-tech]

Summary

• add a persistent global conversation message-text scale matching Android's 70%-200% range and 10% steps
• add a native iOS text-size picker with preview, provisional Cancel/OK behavior, Dynamic Type support, accessibility labels, and constrained-layout scrolling
• scale only primary message body text while preserving reply previews, timestamps, reactions, and attachment labels
• include the preference in migration export/import and localization catalogs
• add normalization, migration, layout, accessibility, and 70%/100%/200% visual regression coverage

Fixes #135

Verification

• 224 static tests passed, 1 skipped
• 34 Swift package tests passed
• 174 shipping app XCTest tests passed
• 21 Model B XCTest tests passed
• shipping post-processed Release ABI/artifact verification passed
• Model B artifact-isolation verification passed
• independent exact-head standards and spec-compliance reviews found no actionable findings
• added-line sensitive-data scan and git diff --check passed

Visual verification

Verified normal and accessibility-width picker renderings plus long-message and reply-bubble renderings at 70%, 100%, and 200%. No clipping or unintended secondary-text scaling was observed.

Risk and rollback

The new preference defaults to 100%, so existing rendering is unchanged until the user selects another value. Removing this PR restores prior behavior; migrated backups without the preference retain the default.

[greptile-apps]

Greptile Summary

Adds a persistent, migration-compatible conversation message-body text scale and a native SwiftUI picker, while leaving secondary message metadata unscaled.

• Stores normalized values from 70% through 200% in 10% increments.
• Applies the scale to primary message text with Dynamic Type support.
• Exports and imports the preference in migration bundles.
• Adds localization, accessibility, layout, migration, and visual regression coverage.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete changed-code failure identified.

The preference is normalized at every persistence boundary, loaded into conversation state, restricted to primary message-body rendering, included symmetrically in migration export and import, and compiled into both app targets.

Important Files Changed

Filename	Overview
Sources/ColumbaApp/Services/SettingsRepository.swift	Adds finite-value normalization, clamping, step rounding, repair, and persistence for the global message-text scale.
Sources/ColumbaApp/Views/Messaging/MessagingView.swift	Loads the persisted scale, presents the picker, saves confirmed changes, and passes the scale into message bubbles.
Sources/ColumbaApp/Views/Messaging/TextSizePickerSheet.swift	Adds a scrollable, Dynamic-Type-aware picker with provisional state, preview, range controls, and accessibility metadata.
Sources/ColumbaApp/Views/Messaging/MessageBubble.swift	Applies the selected scale only to primary message-body text using a body-relative scaled metric.
Sources/ColumbaApp/Services/MigrationExporter.swift	Adds the normalized message-text scale to exported preferences as a double.
Sources/ColumbaApp/Services/MigrationImporter.swift	Extracts settings import into a testable method and restores valid message-text scale preferences through repository normalization.
Columba.xcodeproj/project.pbxproj	Includes the new picker source in both shipping and Model B app targets.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    User[Conversation menu] --> Picker[Text size picker]
    Picker -->|OK| Settings[SettingsRepository]
    Settings --> Defaults[App Group UserDefaults]
    Settings --> ViewState[MessagingView scale state]
    ViewState --> Bubble[MessageBubble primary body]
    Settings --> Exporter[MigrationExporter]
    Importer[MigrationImporter] --> Settings

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_{Reviews (1): Last reviewed commit: "test: calibrate picker rendering bounds" | Re-trigger Greptile}