fix: pick single-file targets in interactive mode

[Dhirenderchoudhary]

The bug

gitpick <file-url> -i died before copying anything:

✔ elayadesign/ai-design-skills blob:main skills/landing-page-design/SKILL.md > ~/.agents/skills/landing-page-design/SKILL.md
⠇ Fetching elayadesign/ai-design-skills...
Error: ENOTDIR: not a directory, scandir '/var/folders/.../SKILL.md'

Fixes #75

Interactive mode scopes its walk to config.path and readdirs it unconditionally, so a pick that resolves to a file gets read as a directory.

It isn't only blob: URLs

A tree: pick crashes identically when the path names a file and that's the normal shape on Bitbucket and Codeberg, whose src/<ref>/<path> URLs look the same for files and folders (transform-url.ts types both as tree). Reproduced on codeberg.org/Codeberg/avatars/src/branch/main/README.md and nrjdalal/picksuite/tree/main/file.txt. So the decision is made on the checkout, not on the URL type — one check covers every host.

What changed

• bin/index.ts: when the picked root isn't a directory there is nothing to browse, so gitpick says so and copies the file the way the plain pick does. --dry-run, the file overwrite guard, --init/--commit, --tree, -q and temp-dir cleanup all behave exactly as they do without -i.
• renderTree hoisted above the interactive block so both paths share it instead of duplicating the file-target rendering.
• Two things the new branch surfaced in the same block: -f never worked in remote interactive mode (only -o did, though the warning names both), and the spinner ignored -q/--tree.
• README.md: one line under Interactive Mode.

Result:

✔ nrjdalal/picksuite blob:main file.txt > out/file.txt
✔ Fetched nrjdalal/picksuite (1 entry)

Note: file.txt is a single file - -i has nothing to browse.
✔ Copied 1 file to out/file.txt

Tests

Six cases in tests/cli.test.ts: blob URL picks the file, tree: URL that resolves to a file, --dry-run copies nothing, refuse-then-overwrite (-o, -f), --tree, -q. All six fail on the unfixed bin/index.ts and pass with it.

-i refuses to start outside a TTY, so the cases run through a small shim that marks stdout as a TTY and hands over to the built CLI. A single-file pick never opens the picker, so nothing reads keys that keeps the tests portable to the Linux/macOS/Windows matrix, unlike allocating a real pty.

• bun run test: 284 pass, 0 fail
• oxfmt --check and oxlint clean