Route /Skills paths to the Files API in databricks fs

[pranavdev022]

Changes

filerForPath now routes dbfs:/Skills/... to the Files API filer, alongside the
existing /Volumes/ branch, instead of falling through to the legacy DBFS filer.

Why

UC Skills are Files-API-native: the server exposes skill bundle bytes at
/api/2.0/fs/files/Skills/<catalog>/<schema>/<skill>/<file>, exactly like Volumes. This
lets users manage a skill bundle with the standard databricks fs commands, e.g.:

databricks fs cp -r ./my-skill dbfs:/Skills/<catalog>/<schema>/my-skill/

fs cp -r walks the local tree and PUTs each file via the Files API (no atomic bundle
endpoint — same as Volumes). The dbfs: scheme is legacy URI naming only; the request
goes to the Files API.

Scope

One-line routing change. No new command, API method, or endpoint — reuses the existing
public Files API, parallel to how /Volumes/ is handled. Shell completion already keys
off the dbfs: scheme, so no completion change is needed.

Tests

Added new tests to cover Volumes and Skills.

[github-actions]

Approval status: pending

/cmd/fs/ - needs approval

8 files changed
Suggested: @renaudhartert-db
Also eligible: @simonfaltum, @hectorcast-db, @parthban-db, @tanmay-db, @Divyansh-db, @tejaskochar-db, @mihaimitrea-db, @chrisst, @rauchy

General files (require maintainer)

6 files changed
Based on git history:

• @renaudhartert-db -- recent work in cmd/fs/, .nextchanges/cli/

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db, @janniklasrose, @lennartkats-db) can approve all areas.
See OWNERS for ownership rules.}

[pranavdev022]

@renaudhartert-db - can you please take a look?
Thanks!

[github-actions]

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Inputs:

• PR number: 6118
• Commit SHA: 97541f25d51db04339831d5eb32c2bcd56b57f19

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