docs: clarify that -e/--extension matches all entry types

[wyf027]

Summary

Clarifies documentation for -e / --extension (#1693): the filter matches any entry whose name ends with the extension, including directories (e.g. clojure.zip/), not only regular files.

Follows maintainer feedback on #1922:

• Short help (-h): minimal — "Filter by extension"
• Long help (--help) and fd.1: note that --type can restrict entry types

Test plan

• cargo clippy -- -D warnings
• Doc-only change (no runtime behavior change)

[wyf027]

@tmccombs Thanks for the review on #1922 — pushed e60582f to address it:

• -h: short help is only `Filter by extension` (details in `--help` / doc comment).
• man: avoids “not just files”; says the filter applies to all entry types and points to `--type`.
• scope: removed accidental `--full-path` doc edits from this branch (those are in docs: clarify --full-path help text (fixes #1686) #1997 only).

CI should stay green. Happy to close this if you prefer updating #1922 instead.

[tmccombs]

I think it would be more clear to say it applies to "both files and directories".

Also, I'd prefer for this to come after teh comment about it being allowed to be used repeatedly.

Same applies to the help text.