fix(ci): send forge provenance for api runs

[bdsqqq]

depot ci run now detects and sends cursor origin forge provenance.

• recognizes github and cursor origin remotes
• adds --forge for explicit selection when both forges are configured
• preserves origin priority for same-forge fork and upstream remotes
• preserves github behavior for explicit repositories without a supported remote

api: depot/api#4693
linear: DEP-6095

[linear-code]

DEP-6095

[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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