Upload every distribution to robostack-<distro> on anaconda.org and prefix.dev; noetic's staging copy moves here

[Tobias-Fischer]

Every distribution uploads its packages directly to robostack-<distro> on both anaconda.org and prefix.dev, instead of a separate mirror job, as discussed in #54. Nothing goes to robostack-staging anymore:

• humble's channel becomes robostack-humble, the one documented for years;
• rolling's and lyrical's anaconda.org channels get populated, so -c robostack-rolling works.

Upload (pixi run rs <distro> upload, run by the staged build workflows):

1. anaconda.org first: rattler-build upload anaconda -o robostack-<distro> --force. The token comes from the ANACONDA_API_TOKEN secret, which the generated build.yaml already passes, and goes in through the environment, never the command line.
2. Then prefix.dev: rattler-build upload prefix -c robostack-<distro> --skip-existing --generate-attestation, with trusted publishing as before.

prefix.dev decides what gets built (skip_existing), so it must never have a package that anaconda.org lacks:

• If anaconda.org fails after its retries, nothing goes to prefix.dev.
• If prefix.dev fails, the next run builds the package again, and --force replaces the anaconda.org copy, so both channels end up with that build.
• A missing token fails the upload.

The builds read prefix.dev. ROBOSTACK_UPLOAD_CHANNEL (a test channel) or none still redirect or skip all uploads, as before.

channel_name and upload_target leave distro.yaml: every distribution's channel is robostack-<distro>, and rs.channel_name() is the one place for that (also used by the ABI check, the stale and build-number lookups, new-distro and import_distro).

Staging copy for noetic: tools/copy_staging_packages.py + the hourly copy-staging-packages.yaml move here from RoboStack/robostack.github.io (RoboStack/robostack.github.io#205 removes them there). They now only copy noetic, which RoboStack/ros-noetic still uploads to robostack-staging, on to robostack-noetic. The job is skipped without its ROBOSTACK_NOETIC_ANACONDA_API_TOKEN secret.

Before merging:

• prefix.dev: robostack-humble and robostack-jazzy are mirrors of anaconda.org today. They need to become regular channels, with Repository Access for this repository (build.yaml, read/write), like rolling and lyrical.
• anaconda.org: create robostack-lyrical (it doesn't exist yet). The robostack-humble, robostack-jazzy and robostack-rolling channels exist.
• Secrets: ANACONDA_API_TOKEN (an account that can upload to all four robostack-<distro> channels) and ROBOSTACK_NOETIC_ANACONDA_API_TOKEN. Then merge Move the channel copy script to the RoboStack monorepo robostack.github.io#205.

After this, the humble and jazzy sync PRs drop channel_name/upload_target from their distro.yaml when they're rebased.

Tests: 6 new upload tests (order, a failed anaconda.org upload, the missing token, the override, none); all 56 tool tests pass, and so does rs check. The README lists both hosts per distribution, the credentials and the noetic copy. Labelled build:humble.

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