Stream log exports row-by-row to avoid unbounded memory buffering

[DeveloperDurp]

Motivation

• The plaintext export endpoint previously loaded all deployment log rows and concatenated them into a single in-memory buffer, which can exhaust server memory for large logs and enable a DoS-style availability issue.
• The goal is to produce the same textual export but without materializing the full result set in process memory.

Description

• Added Repository.ForEachDeploymentLogByDeploymentAsc which streams rows via QueryContext and invokes a callback per db.DeploymentLog to avoid building a large slice. (internal/repository/repository.go).
• Reworked the web handler ExportLogs to write the file header and then stream each formatted log line directly to the http.ResponseWriter using the new ForEachDeploymentLogByDeploymentAsc callback instead of ListDeploymentLogsByDeployment + strings.Builder (removes unbounded buffering). (internal/handler/logs.go).
• Applied the same streaming change to the API handler ExportLogs so both web and API export paths now stream rows row-by-row. (internal/handler/api/logs.go).

Testing

• Ran formatting/linters: gofmt -l and git diff --check on the modified files (passed).
• Attempted to run the TestExportLogs unit tests via go test -run 'TestExportLogs' ./internal/handler ./internal/handler/api, but running the tests is blocked in this environment because template-generated packages (templ outputs) are missing and templ generate cannot be executed here (templ not installed and module proxy access restricted); therefore the export tests could not be executed end-to-end in this session.
• Verified the change compiles locally for the edited files and committed the patch (Stream log exports without buffering).

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Codex Task