feat(map): render MMS images inline in conversation (tincan-orn95)

[quad341]

Summary

• Fetches full MIME body for MMS messages via Attachment:True in BlueZ Message1.Get
• Parses multipart MIME in new _parse_mms_content(): extracts text body and base64-encodes image attachments as [{mime_type, data}]
• Passes attachments as a JSON string through the D-Bus sv dict chain (dbus_service.py → GUI)
• Renders each image inline in the conversation bubble (QLabel + QPixmap, max 300 px wide) beneath the message text
• Treats non-empty attachments as sufficient for display (no BODY_UNAVAILABLE placeholder when image-only MMS)

Tests

• 26-case MIME parsing suite added in tests/tincand/test_parse_mms_content.py (tincan-cq4l6)
• Full suite: 1116 passed, 1 warning

Test plan

• Send an MMS with an image from an iPhone; verify image renders inline in conversation view
• Send a text-only SMS/MMS; verify no regression in text display
• Send a multi-part MMS with text + image; verify both text body and image appear
• Verify image-only MMS (no text body) shows image without "message unavailable" placeholder
• Run pytest — all 1116 tests pass

🤖 Generated with Claude Code

[quad341]

Reviewer finding: request-changes

1 blocker — fix is 2 lines / ruff --fix

F1 [BLOCKER] Ruff violations in tests/tincand/test_parse_mms_content.py

tests/tincand/test_parse_mms_content.py:30:1: I001 Import block is un-sorted or un-formatted
tests/tincand/test_parse_mms_content.py:38:8: F401 `pytest` imported but unused

(Confirmed against pyproject.toml select = ["E", "F", "W", "I"])

Fix: remove import pytest (line 38); run ruff check --fix tests/tincand/test_parse_mms_content.py for the sort. The builder mail said "Ruff clean" but ruff was not run against the test file before submission.

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All other dimensions pass: 1204 tests green, security clean, _parse_mms_content logic correct, D-Bus JSON path guarded, spec met.

Re-submit after the lint fix.