feat: implement gloss orchestration core (lookup + fetch-online)

Two pure-ish helpers and two interactive entry points.

`gloss--orchestrate-fetch-result' is a pure pattern-matcher that
classifies a fetch result into one of five decision symbols. The
ordering matters: definition count gates first, then the error
taxonomy. All-empty falls through to `:error-no-defs' so the user
never sees a silent no-op.

`gloss--lookup-flow' is the orchestration. Cache hit dispatches
straight to display. Cache miss runs a fetch, classifies via the
helper, and either auto-saves the lone definition, prompts the user
to pick, or messages the right error. The `force-fetch' arg lets
`gloss-fetch-online' reuse the same flow without duplicating logic.

`gloss-core-save' is called with the `replace' collision action so
force-fetch over an existing entry replaces it cleanly. On a real
cache miss the entry is fresh, so `replace' is moot — the action
only matters when the term is already there.

`gloss-lookup' and `gloss-fetch-online' are now thin interactive
wrappers around `gloss--lookup-flow'. The remaining stubs (add, edit,
list-terms, stats, reload, drill-export) still raise user-error.

111 tests pass in 0.23s — 98 prior plus 13 new across the two new
files.

0 files changed, 0 insertions, 0 deletions