feat(tb-lf): add share upload command

[trogulja]

Summary

Adds a tb-lf share upload command that posts files to the new DevPortal Shares API (productiveio/devportal#284). Lets us go from "I have an HTML report" to a short shareable URL with one command from the terminal.

tb-lf share upload report.html
tb-lf share upload report.html diagram.png --visibility unlisted --title "Q3 review"
tb-lf share upload bundle/*.html --visibility unlisted --json

Reserves the `share` namespace for upcoming actions (`list`, `delete`, `show`) which will follow as DevPortal exposes the corresponding endpoints.

Implementation

• Enables `multipart` + `stream` features on workspace `reqwest`.
• Adds `DevPortalClient::post_multipart` which posts to the bare DevPortal URL (not the `/spa_api/ai` API base) — Shares is cross-team infrastructure at `/spa_api/shares`.
• Stores `config.url` separately as `devportal_url` on the client so existing `/spa_api/ai/*` paths keep using the AI-prefixed base.
• `mime_for_path` provides explicit Content-Type for common extensions. The DevPortal-side CSP injector only fires on `text/html` / `application/xhtml+xml`, so accurate MIME at upload time controls whether the security policy gets baked in.

Drive-by

Replaced two pre-existing `3.14` literals in `types.rs` tests that clippy 1.93 now flags as `approx_constant`. Per repo CLAUDE.md: don't waste time proving pre-existing — fix it.

Requires

• productiveio/devportal#284 to be merged + deployed before this is usable end-to-end. The CLI compiles and runs without it, but POST will fail.

Test plan

• `cargo build -p tb-lf` — clean
• `cargo clippy -p tb-lf --all-targets -- -D warnings` — clean
• `cargo test -p tb-lf` — 3 passing
• `./target/debug/tb-lf share --help` — shows subcommand
• `./target/debug/tb-lf share upload --help` — shows args
• Once devportal#284 is deployed: `DEVPORTAL_TOKEN=... tb-lf share upload ./output/lazy-output-alpha-report.html --visibility unlisted` returns a working `/s/` URL

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