Commit typed link source to a link when the caret leaves it

[Azganoth]

Summary

Typing [a](b), https://example.com, or <https://example.com> leaves literal text, while pasting the same characters creates a link immediately. The editor presents a state that disagrees with plain-text paste and, for bare URLs, with what the file can hold.

Expected behavior

When the caret leaves a run of text that is exactly valid link source, that run becomes the link it describes, for inline links, autolink literals, and URI autolinks. Because projection re-shows the raw source whenever the caret is inside, the visible text does not change as a result of the conversion.

Text that is not exactly valid link source is unaffected. \[a](b) stays literal.

Related context

• Related issues or pull requests: Typed link source survives the save only when it is not followed by a space #234 established that the two typed paths now agree, and deferred this decision.
• Documentation, decisions, or prior investigation: docs/specification.md, Inline Content.

Done when

• Typed inline-link, autolink-literal, and URI-autolink source commits to a link on caret-leave.
• Enter and Shift+Enter commit it through the existing projection finalization path.
• Backslash-escaped source stays literal.
• Typing and plain-text paste of the same source produce the same document.
• docs/specification.md describes the rule.

Notes

Implementation direction

Reuse projection's existing validity check and commit trigger rather than adding an input rule. The commit path for an edited projected link already turns valid source into a link; this extends the same rule to a run that was never a link.

Out of scope

• An eager commit on a boundary character. Caret-leave is the uniform trigger; revisit only if it feels sluggish in use.