ci(stagex): build parser_http_server and parser_grpc_server images

[pepe-anchor]

Why

PRS-581 deploys parser_http_server as the TVC pivot. The stagex "TVC deployment details" step hardcodes parser_app, so it is the only binary that ever gets a reproducible executable digest and a paste-ready deploy block. Without this, the pivot cannot be deployed or probed at all, which blocks the /dev/nsm reachability probe and every later step in the stack.

Landing it early so image builds are never the thing holding the stack up.

What

• Adds parser_grpc_server and parser_http_server to the stagex build matrix.
• Generalizes the deployment-details step over the matrix target: TARGET_NAME env, per-target container URL, per-target extract container and binary path, per-target deploy-md and release-note sentinels so parallel matrix legs cannot clobber each other's release body edits.
• Adds images/parser_http_server/Containerfile, mirroring parser_app's. It keeps --features "vsock ${CHAIN_FEATURES}", which is load-bearing: vsock switches qos_core::EPHEMERAL_KEY_FILE to the in-enclave path, and without it the deployed pivot panics at startup and TVC reports 0 healthy replicas.

Two changes from the x402 branch were deliberately NOT taken, because they belong to other PRs:

• the PR-label rename ci:stagex to stagex. Main's label is kept.
• qos_version="v2026.2.6". Main's 0.12.0 is kept; the QOS bump is its own PR in this stack.

Test evidence

The stagex path only runs on a labelled PR, so this needs the ci:stagex label to be validated. What was verified locally:

python3 -c "import yaml; yaml.safe_load(open('.github/workflows/stagex.yml'))"  -> parses
grep 'label.name' stagex.yml  -> 'ci:stagex'  (unchanged from main)
grep -c 'v2026.2.6' stagex.yml -> 0

I have NOT run the stagex build itself. Please add ci:stagex and confirm all matrix legs go green, including the two new ones, before merging.

Rollback

Revert the commit. CI-only change plus one new Containerfile; nothing is deployed by merging it.

Linear

PRS-581

Stack position: independent of the rest of the stack, based on main. Can merge in any order.

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