chore(composer): drop the dead src/ PSR-4 autoload mapping

[Herm71]

Closes #24.

What

Removes the autoload block from composer.json:

"autoload": {
    "psr-4": {
        "UCSC\\UcscCommunicationsFunctionality\\": "src/"
    }
}

autoload-dev (UCSC\UcscCommunicationsFunctionality\Tests\ → tests/) is kept — the PHPUnit suite genuinely uses it.

Why

Option A from the issue, which is the one it recommends. The mapping was inert on three counts:

1. No src/ directory exists.
2. No namespaced classes exist — all code is procedural, loaded by require_once from plugin.php.
3. plugin.php never requires vendor/autoload.php, and vendor/ is gitignored and not shipped by npm run zip.

So it loaded nothing and broke nothing, but advertised an architecture the plugin doesn't have.

Option B (build into src/) was rejected as out of scope: it means restructuring all current procedural code, requiring the autoloader at runtime, and shipping vendor/ or a generated production autoloader in the release zip — otherwise the plugin fatals on activation. If classes land later, the autoload block comes back in the same commit as the first class, along with that packaging work.

Docs

• CLAUDE.md — the "Namespace / autoloading" section now describes the procedural reality and records what re-adding autoloading would require; the stale Known quirks entry is removed.
• ROADMAP.md — the Deferred / not planned entry is replaced with a "Resolved after the audit" record carrying the cause and fix, matching how the other nine items are kept.

Acceptance criteria

• composer.json and the on-disk layout agree — the mapping is gone.
• composer run lint still exits 0 (4/4 files, zero errors, zero warnings).
• CLAUDE.md and ROADMAP.md entries updated.

Verification

composer run lint    → exits 0, zero errors, zero warnings
phpunit              → OK (22 tests, 38 assertions)
composer validate    → ./composer.json is valid (lock file unaffected)

PHPUnit was run via the container fallback documented in CLAUDE.md, since the local php8.5 lacks ext-mbstring.

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