Add @mention support to messaging (compose autocomplete, tappable render, self-mention notification)

[Copilot]

Implements cross-platform @mention feature per meshtastic/design#21. Wire format is @!<8-hex-id> (e.g. @!deadbeef) matching Android/Web exactly.

Core parser — Meshtastic/Helpers/MentionParser.swift

• activeMentionQuery(in:) — detects in-progress @<query> at end of text; returns nil if followed by ! (resolved) or whitespace (ended)
• insertMentionToken(into:user:) — replaces @<partial> suffix with @!<hexId> using Int64.toHex()
• resolveMentions(in:context:) — at render time, converts @!<hex> tokens to [@DisplayName](meshtastic:///nodes?nodenum=<num>) markdown links; resolves live from SwiftData — name changes reflect without re-sending
• containsMention(of:in:) — exact wire-format self-mention check for notifications

Compose — TextMessageField.swift + MentionAutocomplete.swift

• MentionAutocomplete overlay queries all NodeInfoEntity via @Query, filters by long name / short name / user ID, caps at 10 results, shows CircleText + name
• Integrated into both the iOS 17 TextField path and the iOS 18+ FormattingComposeArea (TextEditor) path
• Selection inserts the hex token; state clears on send/dismiss/position-request

Render — MessageText.swift

• Calls resolveMentions before AttributedString(markdown:) — mentions render as tappable underlined links showing current node display name
• handleURL intercepts meshtastic:///nodes?nodenum= and calls appState.router.navigateToNodeDetail(nodeNum:) for deep-link navigation

Notifications — MeshPackets.swift

• Channel messages always trigger a local notification when the connected node's own ID is mentioned, regardless of per-channel mute setting

Docs — docs/user/messages.md

• Added ## @Mentions section covering compose flow, tappable links, notification behaviour, and wire-format note

How is this tested?

MeshtasticTests/MentionParserTests.swift — 23 unit tests using Swift Testing covering all MentionParser functions: regex matching, node-num extraction, active-query detection edge cases (resolved token, trailing space, empty string), token insertion, and self-mention detection.

Screenshots/Videos (when applicable)

UI changes are in the compose field (autocomplete list on @) and message bubbles (tappable mention links). Screenshots to be added by reviewer if needed.

Checklist

• My code adheres to the project's coding and style guidelines.
• I have conducted a self-review of my code.
• I have commented my code, particularly in complex areas.
• I have verified whether these changes require updates to the in-app documentation under docs/user/ or docs/developer/, and updated accordingly (see copilot-instructions.md for the view → doc page mapping). If no doc update is needed, add the skip-docs-check label.
• I have tested the change to ensure that it works as intended.

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[RCGV1]

I found a compile-blocker plus two mention handling issues that look worth fixing before this is ready. Details inline.

[RCGV1]

This PR currently does not compile. Running xcodebuild test -project Meshtastic.xcodeproj -scheme Meshtastic -destination 'platform=iOS Simulator,name=iPhone 17' -only-testing:MeshtasticTests/MentionParserTests fails with Cannot find 'MentionAutocomplete' in scope and Cannot find 'MentionParser' in scope. I also checked Meshtastic.xcodeproj/project.pbxproj and it has no references to MentionAutocomplete, MentionParser, or MentionParserTests, so the new source/test files are never added to the Xcode targets. Please add these files to the Meshtastic and MeshtasticTests targets; otherwise the app target fails before the mention tests can run.

[RCGV1]

This regex still matches the prefix of a longer token, e.g. @!deadbeef00 is treated as a mention of @!deadbeef, even though the documented wire format above says exactly 8 lowercase hex digits. The same prefix problem exists in containsMention via text.contains, so a malformed longer token can trigger a self-mention notification for the wrong node. Please require a non-hex/token boundary after the eighth digit, or reuse parsed bounded ranges for notification detection, and update the tooLongHex_matchesFirst8 test to reject this case.

[RCGV1]

displayName comes from mesh data, so it can contain Markdown control characters such as ], [, (, ), or \. Interpolating it directly into Markdown link text can make AttributedString(markdown:) fail or create unintended Markdown/link structure for every message that mentions that node. Please escape the link text before interpolation, or build the attributed link without round-tripping through Markdown.