refactor(cli): remove agent package import from send.go, attach.go, models.go

[proboscis]

Summary

Remove unnecessary coupling between CLI files and the agent package by:

• Replacing agent.AgentOpenCode with "opencode" string literal in send.go and attach.go
• Replacing agent.OpenCodeServerPortStart with local constant 4096 in models.go
• Adding semgrep rule to prevent future agent package imports in these files

Changes Made

File	Change
send.go	Replaced run.Agent == string(agent.AgentOpenCode) with run.Agent == "opencode", removed agent import
attach.go	Replaced resp.Agent == string(agent.AgentOpenCode) with resp.Agent == "opencode", removed agent import
models.go	Replaced agent.OpenCodeServerPortStart with local constant 4096, removed agent import
.semgrep/architecture.yaml	Added cli-no-agent-import-in-send-attach-models rule

Acceptance Criteria Verification

• send.go: Replace agent.AgentOpenCode with string literal "opencode"
• attach.go: Replace agent.AgentOpenCode with string literal "opencode"
• models.go: Move port constant to local constant (value 4096)
• Remove agent import from all three files
• Add semgrep rule blocking send.go/attach.go/models.go from importing agent package
• go build ./... passes
• go test ./internal/... passes
• make lint passes (semgrep 0 findings)

Evidence

Build passes

$ go build ./...
(no output - success)

Tests pass

$ go test ./internal/...
ok      github.com/s22625/orch/internal/agent     0.760s
ok      github.com/s22625/orch/internal/cli       4.883s
ok      github.com/s22625/orch/internal/config    3.896s
ok      github.com/s22625/orch/internal/daemon    3.159s
ok      github.com/s22625/orch/internal/git       9.321s
ok      github.com/s22625/orch/internal/github    0.687s
ok      github.com/s22625/orch/internal/model     1.729s
ok      github.com/s22625/orch/internal/monitor   2.353s
ok      github.com/s22625/orch/internal/multiplexer 1.338s
ok      github.com/s22625/orch/internal/notify    2.322s
ok      github.com/s22625/orch/internal/query     1.684s
ok      github.com/s22625/orch/internal/store/file 1.491s
ok      github.com/s22625/orch/internal/tmux      1.210s
ok      github.com/s22625/orch/internal/xdg       0.707s

Lint passes

$ make lint
semgrep --error --config .semgrep/ ./internal/cli/
✅ Scan completed successfully.
 • Findings: 0 (0 blocking)
 • Rules run: 8
 • Targets scanned: 29

Closes: orch-413