Add CLI command to define/author catalog skillsets (tink skillset define)

[jon-devlapaz]

Problem

Currently, Tink has commands to inspect sources (tink inspect) and install skillsets (tink skillset add), but has no command to create or author a pinned skillset definition ($TINK_HOME/catalog/by-skillset/<name>-skillset/meta.json).

Users and coding agents must manually construct JSON files and write them to internal Tink home paths using raw filesystem operations. This leads to:

• Syntax and schema errors (e.g. source_root vs sourceRoot, missing required keys).
• Missing directory creation errors.
• Lack of preflight validation until tink skillset add is executed.
• Increased friction for agent automation.

Proposed change

Introduce a tink skillset define <NAME-skillset> command to author or update definitions in $TINK_HOME/catalog/by-skillset/<name>-skillset/meta.json with upfront validation:

tink skillset define NAME-skillset \
  --source <GIT_URL> \
  --revision <SHA> \
  --source-root <DIR> \
  --members <MEMBER1,MEMBER2...>

Options to consider:

• --force / --overwrite to update an existing definition.
• Direct synthesis from inspection or an inspect candidate.
• Enforce the -skillset canonical name suffix.
• Validate that the revision is a 40-character commit hash and sourceRoot is normalized.

Acceptance

• tink skillset define my-skillset --source ... --revision ... --source-root ... --members ... writes a valid meta.json to $TINK_HOME/catalog/by-skillset/my-skillset/meta.json.
• Refuses non-canonical names not ending in -skillset.
• Validates sourceRoot and input format before writing.
• Refuses to overwrite existing definition unless --force is specified.
• Works cleanly in scripted/agent environments.

[jon-devlapaz]

Closing backlog issue to converge to git-golden state. Re-open if needed for future iterations.