OSC 133 support

[nindanaoto]

Fix #28.
Add the ability to retrieve the output of the last completed command using OSC 133 (FinalTerm) shell integration semantic markers. This is exposed through:

• A TalkBack custom accessibility action ("Read Last Output") that announces the output via announceForAccessibility
• A public API (TerminalEmulator.getLastCommandOutput()) that ConnectBot uses to expose this in a menu item

How it works

The implementation scans backward through terminal lines (scrollback + visible) to find:

1. The most recent COMMAND_FINISHED marker (OSC 133;D)
2. The matching COMMAND_INPUT marker (OSC 133;B) with the same promptId
3. All lines between them, which are the command output

Changes

AccessibilityOverlay.kt

• Add getLastCommandOutput(lines) internal function that extracts the last command's output text from semantic segments
• Add "Read Last Output" custom accessibility action that calls getLastCommandOutput() and announces the result via TalkBack

TerminalEmulator.kt

• Add getLastCommandOutput(): String? to the public TerminalEmulator sealed interface
• Implement in TerminalEmulatorImpl by reading the current snapshot's scrollback + visible lines and delegating to getLastCommandOutput(lines)

OscParser.kt

• Move COMMAND_INPUT segment creation from C time (OSC 133;C) to B time (OSC 133;B). In real shell integration, the user presses Enter before C is sent, which scrolls the terminal. Since libvterm uses screen-relative cursor positions, the cursor row stays the same after scroll while the column resets to 0, causing the old column comparison to always fail. Creating the segment at B time ensures it is placed on the correct screen row and gets properly shifted by pushScrollbackLine along with the text content.

ReadLastOutputTest.kt (new)

• 8 unit tests covering: basic output, no finished marker, no input marker, empty output, multiple commands, multi-line output, trailing
  whitespace, and scrollback scenarios

OscParserTest.kt

• Update testOsc133PromptFlow for new behavior (B now emits both PROMPT and COMMAND_INPUT)
• Add testOsc133PromptFlowCrossRow covering the realistic scenario where scroll keeps the cursor at the same screen-relative row

Unit Tests

• ReadLastOutputTest — 8 tests covering getLastCommandOutput() logic
• OscParserTest.testOsc133PromptFlow — same-row OSC 133 flow
• OscParserTest.testOsc133PromptFlowCrossRow — cross-scroll OSC 133 flow (the real-world case)
• Manual test on device with bash OSC 133 shell integration: run commands, verify TalkBack action and public API both return correct output