P4: Exotic malformed Markdown link inputs

[RE-codes]

Story

As a vault user pasting in malformed link syntax, I expect Obsidian's native handling — the plugin should not crash or do something surprising.

Tasks

• Add a few exotic malformed examples ([[](url), [[](#h, [](#), [](, []()).
• Verify the plugin either bails out or matches Obsidian's native handling without errors.
• Where Obsidian's behavior is not navigation, the plugin must not navigate either.
• Add unit tests for any input that previously caused a crash.

Acceptance Criteria

• No crashes on malformed inputs.
• Behavior matches Obsidian native (no navigation, no error).
• Matrix P4 row updated.

References

• Parent epic: Epic: P4 Lower-Priority Readiness #93