fix(scripts): close unterminated quote that broke serve_concurrency_gate.sh parsing

[alpineQ]

Summary

fe031717 (daemon crate move) left fail "build first: cargo build --release -p hipfire-daemon without its closing quote, so bash fails to parse the entire script (syntax error near unexpected token '(', reported at line 174 inside the python heredoc) and the gate exits 2 before ever starting a server. One-character fix; bash -n scripts/serve_concurrency_gate.sh is clean after.

Side note, not addressed here: the gate also needs bc on PATH (absent on NixOS by default) — flagging in case a POSIX-arithmetic rewrite is preferred over the dependency.

Which crate(s) does this touch?

• docs / CI / scripts

Test plan

• bash -n scripts/serve_concurrency_gate.sh clean (was: syntax error, exit 2)
• Gate parses and runs end-to-end again
• Change gate run and telemetry pasted below

change_gate telemetry

**change_gate: PASS**

host gfx=`gfx1100` rocm=`6.18.37` models_dir=`/home/alpineq/.hipfire/models` · `80a572c824dcbbcdddac1cc5f6d1a7e91d7c4dd6`..`f76d3c3f1953c7c7c67b8d4baa680441fa7f0c6e` dirty · est=0.0min actual=0.0s

### Routes RUN
| route | status | duration |
| ----- | ------ | -------- |
| —     | —      | —        |

### Routes NOT RUN
| route | reason |
| ----- | ------ |
| —     | —      |

_Blocked or excluded routes mean coverage is incomplete — this report is not an admission that unrun surfaces are safe._