test: cover the day cache and cli dispatch directly

[only-cli]

First step on test coverage: the two modules with the thinnest direct coverage. src/cache.js had no test importing it, and src/cli.js was exercised only through its auth commands in tests/cli-auth.test.js.

tests/cache.test.js (7 tests)

The network is a local HTTP proxy that records every request, reached through HTTP_PROXY the same way the fetch tests do, so "the network was never asked" is asserted rather than assumed. Nothing leaves the machine.

• A miss fetches, parses, and writes the file under <kind>/<host><ext>.
• A fresh file is served from disk and the proxy sees zero requests.
• A file older than a day is refetched and replaced.
• A body the parser rejects is never written, so a block page cannot poison the cache.
• A stale good copy survives a refetch whose body the parser rejects.
• A cache directory that cannot be created costs only the refetch, twice in a row.
• A URL with no extension caches under the bare host, and kinds do not share directories.

tests/cli.test.js (18 tests)

Each case spawns the real binary against a throwaway OC_HOME. The page under test is seeded straight into a session file, so read, next, find, and do on text all have something to answer with, and no test fetches.

• No command, --help, and -h print the usage and exit 0.
• The usage names every dispatchable command exactly once, so the help text and the dispatch table cannot drift apart silently.
• An unknown first word fails in one line pointing at --help.
• A site name is tried as a shortcut before it is called unknown, so a wrong verb reports the site's verbs.
• --budget must be a positive number and --session must be a safe filename, both checked before any command runs.
• read, next, find, and do with nothing open all say to run open first.
• open and raw with no URL print a usage line.
• read <n> prints the region, and a bad number gives usage rather than a stack trace.
• next reports the end of a page that fit in one render.
• find joins the rest of argv into one query, and fails with usage on none.
• do on a text number reads it in place; a recording proxy proves no request left.
• do with no number, or a number the page lacks, fails in one line.
• fill, submit, back, and session fail with the same one-line message naming themselves.
• sites lists the bundled shortcuts.
• Flags work before or after the command.

Verification

Every test was checked against a deliberate break in the code it guards, each caught by the test meant to catch it:

Break	Caught by
TTL check removed	fresh file served from disk
write moved before parse	both poison tests
--budget check removed	budget validation
shortcut lookup removed	site name before unknown
fill wired to submit	planned commands name themselves
find joins argv with ''	find joins argv

Full suite: 212 passing (was 188), offline, no new dependencies.