feat: add ObsidianFindIncomingLinks and ObsidianFindOutgoingLinks commands

[metalelf0]

What does the PR do?

Adds two new note-context commands for surfacing and converting unlinked plain-text mentions:

• :Obsidian incoming_links / :ObsidianFindIncomingLinks — scans all cached vault notes for plain-text mentions of the current note's title or aliases; opens a picker to select matches and convert them to links in the target files.
• :Obsidian outgoing_links / :ObsidianFindOutgoingLinks — scans the current buffer for plain-text mentions of other vault notes (by title or alias); opens a picker to select and convert matches to links in-place.

Both commands support multi-select (<Tab> to toggle, <CR> to apply all selected).

Implementation notes

• No new scan logic. Both commands wire through the existing note/link_suggestion module (symbols, find, find_in_line). All skip rules (existing links, code fences, inline code, frontmatter, tags, bare URLs) are inherited for free.
• Incoming links iterates cache.notes.all(), applies a fast raw-string pre-filter before full note parse, then scans with find_in_line. On confirm it bufadd/bufloads the target file, applies nvim_buf_set_text, writes, and unloads if it was not previously open.
• Outgoing links calls link_suggestion.find(note) on the current buffer and delegates conversion to the existing actions.link_suggestion.
• Respects configured link.style / link.format.
• Errors gracefully when cache is not enabled/warm.

Files changed

File	Change
lua/obsidian/commands/incoming_links.lua	New command
lua/obsidian/commands/outgoing_links.lua	New command
lua/obsidian/commands/init.lua	Registered both as note_action = true
lua/obsidian/commands/init-legacy.lua	Added ObsidianFindIncomingLinks / ObsidianFindOutgoingLinks legacy aliases
tests/test_find_links.lua	7 new tests
CHANGELOG.md / README.md	Updated

Screenshots

Picker UI is identical to :Obsidian backlinks — standard picker with preview, multi-select via <Tab>.

PR Checklist

• The PR contains a description of the changes
• I read the [CONTRIBUTING.md] file
• The CHANGELOG.md is updated
• The changes are documented in the README.md file
• The code complies with make chores (for style, lint, types, and tests)