feat: add true color (24-bit RGB) support to MicronColor via FT/BT commands

[torlando-tech]

Extend Micron markup to support full 24-bit true color alongside the
existing 3-char (12-bit) hex and grayscale formats. The new syntax uses
FTrrggbb for foreground and BTrrggbb for background, keeping full
backward compatibility with existing Fxxx/Bxxx shorthand.

https://claude.ai/code/session_015rjJisX2XNt331xgXdFbB9

[sentry]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[greptile-apps]

Greptile Summary

This PR extends Micron inline markup with 24-bit true color via FTrrggbb / BTrrggbb commands, keeping full backward compatibility with the existing 3-char shorthand and grayscale formats.

• MicronColor gains parseTrueColor() and exposes TRUE_COLOR_LEN = 6 as internal so the parser can share the constant rather than duplicate it.
• MicronParser extracts the color-parsing logic into parseForegroundOrBackground(), which checks for a T prefix, dispatches to true-color parsing, and returns null immediately on a malformed true-color marker — the T-leaks-into-output issue flagged in the previous review round is now correctly handled.
• Test coverage is thorough: boundary values, multi-line style persistence, reset commands, mixed format use, and direct unit tests of parseTrueColor.

Confidence Score: 5/5

Safe to merge — the change is additive, backward-compatible, and the previously identified T-leak and constant-duplication concerns are both resolved.

The true-color dispatch is correct, the malformed-command fallback returns null cleanly instead of leaking T into the output, TRUE_COLOR_LEN is now a single internal constant shared between files, and the 13 new tests cover the important cases. No regressions to the existing 3-char or grayscale paths were introduced.

No files require special attention.

Important Files Changed

Filename	Overview
micron/src/main/java/com/lxmf/messenger/micron/MicronColor.kt	Adds parseTrueColor() for 6-char hex strings and promotes TRUE_COLOR_LEN to internal so MicronParser can reference a single source of truth.
micron/src/main/java/com/lxmf/messenger/micron/MicronParser.kt	Refactors F/B color branches into parseForegroundOrBackground(), which dispatches to the true-color path on T and correctly gates the 3-char fallback so a T prefix never leaks into the output stream.
micron/src/test/java/com/lxmf/messenger/micron/MicronParserTest.kt	Adds 13 targeted tests covering foreground/background true color, boundary values (black/white), multi-line persistence, reset commands, mixed 3-char/6-char use, and parseTrueColor edge cases directly.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["backtick command: F or B"] --> B["parseForegroundOrBackground()"]
    B --> C{next char == 'T'?}
    C -- yes --> D{colorStart + 6 <= line.length?}
    D -- yes --> E["extract 6 chars\nMicronColor.parseTrueColor()"]
    E --> F{color != null?}
    F -- yes --> G["FormatResult with\ntrue-color Hex(r,g,b)"]
    F -- no --> H["return null\n(malformed FTxxxxxx)"]
    D -- no --> H
    C -- no --> I{afterCmd + 3 <= line.length?}
    I -- yes --> J["extract 3 chars\nMicronColor.parse()"]
    J --> K{color != null?}
    K -- yes --> L["FormatResult with\n3-char Hex or Grayscale"]
    K -- no --> M["return null"]
    I -- no --> M

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_{Reviews (2): Last reviewed commit: "chore(greptile): iteration 1 — applied 2..." | Re-trigger Greptile}