docs: fix P2/P3 typos and syntax errors from drift sweep (#28101) - #28157

## Summary

High-confidence textual subset of the DOCS-637 **P2/P3** drift batch (31
findings total). These 8 fixes are pure typo / grammar / syntax
corrections verified directly against the doc source, so they carry no
risk of misreconstructed command output.

## Changes (6 files)

| Page | Fix |
|------|-----|
| `docs/admin/templates/extending-templates/variables.md` | Remove
doubled word: "file in in the template directory" → "file in the
template directory". |
| `docs/admin/networking/port-forwarding.md` | Grammar: heading "From an
coder_app resource" → "From a coder_app resource". |
| `docs/user-guides/workspace-access/index.md` | Malformed heading
"Through with the CLI" → "Through the CLI". |
| `docs/about/contributing/modules.md` | Conventional-commit example
missing the required space: `feat(git-clone):add` → `feat(git-clone):
add`. |
| `docs/ai-coder/tasks-migration.md` | Add missing closing double-quotes
on Terraform `source`/`version` in two snippets that would fail
`terraform` parsing. |
| `docs/admin/users/idp-sync.md` | Role Sync section said "group sync
settings" (copy-paste from the Group Sync section); remove an invalid
trailing comma from a JSON output example. |

## Deferred (remaining ~23 P2/P3 items, not in this PR)

The rest of the batch is stale **command-output** samples (column/schema
changes, sample values) and items that need a content decision (e.g.
`--psk` now deprecated in favor of `--key`; `--address` deprecated; an
undocumented retention flag). Those need live-output reconstruction or a
call on direction, so they're left for follow-up work, consistent with
the issue's "handle after the P0/P1 fixes land" guidance. One catalog
row (`reverse-proxy-nginx.md:57`, certbot `ws=apache`) is already
handled by #28086 and is excluded here.

Linear: https://linear.app/codercom/issue/DOCS-646

> This PR was created with AI assistance (Coder Agents).

(cherry picked from commit 1d189cc)