docs(readme): document mgit to the docs standard

README.md

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+# mopac-gitea-go
+
+A 100% Go client library and CLI (`mgit`) for the Gitea API (v1).
+Replaces shell/tea glue for every forge operation the MOPAC verticals
+need: one static binary, zero third-party modules (stdlib only),
+machine-parseable JSON output, and a token that never appears in flags,
+logs, or error strings. Built for the harness PR flow: branch list ->
+commit status -> PR create/list/merge.
+
+Status: 2026-08-29 — v0 complete and green: repo create/list/show,
+branch list, commit statuses (report + combined), pull requests
+(create/list/show/merge, all five merge styles), token-scoped auth via
+`GITEA_URL`/`GITEA_KEY`, 0600 env-file config, `-o json` on every
+command, exit codes 0/1/2 with one-line API-error stderr. Built and
+tested entirely against a fake Gitea (unit suite + end-to-end smoke);
+the live forge (git.knownelement.com) attaches with zero code change
+via `GITEA_URL`/`GITEA_KEY`.
+
+## Architecture
+
+```mermaid
+flowchart LR
+    subgraph host[Host]
+        M[mgit CLI\nbin/mgit] --config 0600 env --> M
+        S[smoke/smoke.sh]
+    end
+    subgraph docker[Digest-pinned Docker builder — ALL dev]
+        B[go build / vet / test]
+        F[smoke/fakegitea\nstateful in-memory Gitea]
+    end
+    subgraph wire[Library: package gitea]
+        C[Client\nAuthorization: token header only]
+    end
+    M --> C
+    C --> F
+    C -.-> R[(real Gitea\ngit.knownelement.com)]
+    S --> B
+    S --> F
+```
+
+All compilation, vetting, and testing runs inside the digest-pinned
+`golang:1.26-bookworm` builder (`./dev.sh`); the host never runs a Go
+toolchain. Tests and smoke talk only to the in-process/containerized
+fake; the real forge is never contacted by the test suite.
+
+## Quickstart (verified against the fake)
+
+This is the exact flow the smoke run (`./dev.sh smoke`) executes:
+
+```sh
+./dev.sh check          # build + vet + test inside the Docker builder
+./dev.sh smoke          # boots fake Gitea on 127.0.0.1:8602, drives bin/mgit
+
+# against a real forge instead:
+export GITEA_URL=https://git.knownelement.com
+export GITEA_KEY=<api token>            # or: --config ~/.config/mgit/env (0600)
+
+mgit repo create -n vertical-x --owner ukrrs --desc "one vertical" --private --auto-init
+mgit repo list                          # your repos
+mgit repo list --owner ukrrs            # an org's / user's repos
+mgit repo show ukrrs/Mopac-gitea-go
+mgit branch list ukrrs/MOPAC
+mgit status create ukrrs/MOPAC feat/quota --state success \
+    --context ci/lint --description "lint clean" --target-url https://ci.example/run/1
+mgit status list ukrrs/MOPAC feat/quota          # combined + per-check
+mgit pr create ukrrs/MOPAC --title "Quota accounting" --body - \
+    --base main --head feat/quota <<'EOF'
+## Scope
+- usage accounting per acting identity
+EOF
+mgit pr list ukrrs/MOPAC                          # open by default
+mgit pr list ukrrs/MOPAC --state all
+mgit pr show ukrrs/MOPAC 1
+mgit pr merge ukrrs/MOPAC 1 --do squash
+```
+
+Add `-o json` to any command for machine output. REF arguments accept
+anything the server resolves (full or short sha, branch, tag); PR head
+may be `branch` or `owner:branch` (fork syntax).
+
+## Command reference
+
+| Command | Effect | Key flags |
+|---|---|---|
+| `repo create -n NAME` | create repo (under your account, or an org) | `--owner ORG`, `--desc`, `--private`, `--auto-init`, `--default-branch` |
+| `repo list` | list repos | `--owner OWNER` (default: yours) |
+| `repo show OWNER/REPO` | one repo | |
+| `branch list OWNER/REPO` | branches with tip shas | |
+| `status create OWNER/REPO REF` | report a commit status | `--state success\|pending\|error\|failure`, `--context`, `--description`, `--target-url` |
+| `status list OWNER/REPO REF` | combined status + latest per check | |
+| `pr create OWNER/REPO` | open a PR | `--title`, `--body FILE\|-`, `--base`, `--head` |
+| `pr list OWNER/REPO` | list PRs (open by default) | `--state open\|closed\|all` |
+| `pr show OWNER/REPO NUMBER` | one PR with body | |
+| `pr merge OWNER/REPO NUMBER` | merge an open PR | `--do merge\|rebase\|rebase-merge\|squash\|fast-forward` |
+| `help` | usage | |
+
+Flags may appear before or after positionals (`mgit pr merge
+ukrrs/MOPAC 1 --do squash` parses).
+
+## Configuration
+
+| Source | Keys | Discipline |
+|---|---|---|
+| env vars | `GITEA_URL`, `GITEA_KEY` | wins over the file |
+| `--config PATH` (or `MGIT_CONFIG`, or `~/.config/mgit/env`) | same keys | must be 0600 or stricter; refused before any read |
+
+The token travels ONLY in the `Authorization: token` header. Response
+bodies are never surfaced in error strings — the fake Gitea deliberately
+echoes the presented token back in every error body, and the suite plus
+the smoke redaction pass prove it appears nowhere else.
+
+## Library
+
+```go
+import "git.knownelement.com/ukrrs/mopac-gitea-go/gitea"
+
+c := gitea.New(gitea.Config{BaseURL: url, Token: key})
+prs, err := c.ListPullRequests(ctx, "ukrrs", "MOPAC", gitea.PRStateOpen)
+err := c.MergePullRequest(ctx, "ukrrs", "MOPAC", prs[0].Number, gitea.MergeParams{Do: gitea.MergeSquash})
+```
+
+Sentinel errors (`ErrAuth`, `ErrNotFound`, `ErrValidation`, `ErrServer`,
+`ErrUnreachable`, `ErrMalformedResponse`) wrap-check with `errors.Is`;
+every API failure carries an `http NNN` code in its one-line message.
+This is the surface the harness turns use for their PR flow — no
+copy-paste, no shell parsing.
+
+## Development
+
+```sh
+./dev.sh build|vet|test|check|smoke|shell   # everything runs in the digest-pinned builder
+```
+
+The fake Gitea (`internal/fakegitea`) implements exactly the endpoints
+the client uses, records every request for round-trip assertions,
+honors `FailSpec` for pinned error responses, and maintains real
+semantics: latest-status-per-context folding, worst-of combined status,
+short-sha resolution, merge-style validation, 409 on duplicate open PRs
+and re-merges.
+
+## License
+
+AGPLv3 (see LICENSE).